THE FISHES OF THE DEEP SEA.
The knowledge of the existence of deep-sea fishes is one of the
recent discoveries of ichthyology. It is only about twenty years ago
that, from the evidence afforded by the anatomical structure of a
few singular fishes obtained in the North Atlantic, an opinion was
expressed that these fishes inhabited great depths of the ocean, and
that their organisation was specially adapted for living under the
physical abyssal conditions. These fishes agreed in the character
of their connective tissue, which was so extremely weak as to yield
to, and to break under, the slightest pressure, so that the greatest
difficulty is experienced to preserve their body in its continuity.
Another singular circumstance was, that some of the specimens were
picked up floating on the surface of the water, having met their
deaths whilst engaged in swallowing or digesting another fish not much
inferior or even superior in size to themselves.
The first peculiarity was accounted for by the fact that, if those
fishes really inhabited the great depths supposed, their removal from
the enormous pressure under which they lived would be accompanied by
such an expansion of gases within their tissues as to rupture them, and
to cause a separation of the parts which had been held together by the
pressure. The second circumstance was explained thus:--A raptatorial
fish organised to live at a depth of between 500 and 800 fathoms seizes
another usually inhabiting a depth of between 300 and 500 fathoms. In
its struggles to escape, the fish seized, nearly as large or strong as
the attacking fish, carries the latter out of its depth into a higher
stratum, where the diminished pressure causes such an expansion of
gases as to make the destroyer with its victim rise with increasing
rapidity towards the surface, which they reach dead or in a dying
condition. Specimens in this condition are not rarely picked up; and
as, of course, comparatively few can by accident fall into the hands of
naturalists, occurrences of the kind related must happen very often.
Thus, the existence of fishes peculiarly adapted for the deep sea has
been a fact maintained and admitted for some time in Ichthyology; and
as the same genera and species were found at very distant parts of
the ocean, it was further stated that those Deep-sea fishes were not
limited in their range, and that, consequently, the physical conditions
of the depths of the ocean must be the same or nearly the same over
the whole globe. That Deep-sea fishes were not of a peculiar order,
but chiefly modified forms of surface types, was another conclusion
arrived at from the sporadic evidence collected during the period which
preceded systematic deep-sea dredging.
However, nothing was positively known as to the exact depths inhabited
by those fishes until observations were made during the voyage of
H.M.S. “Challenger.” The results obtained by this expedition afforded a
surer and more extended basis for our knowledge of Deep-sea fishes.
The physical conditions of the deep sea, which must affect the
organisation and distribution of fishes, are the following:--
1. Absence of sunlight. Probably the rays of the sun do not penetrate
to, and certainly do not extend beyond, a depth of 200 fathoms,
therefore we may consider this to be the depth where the Deep-sea
fauna commences. Absence of light is, of necessity, accompanied by
modifications of the organs of vision and by simplification of colours.
2. The absence of sunlight is in some measure compensated for by the
presence of phosphorescent light, produced by many marine animals, and
also by numerous Deep-sea fishes.
3. Depression and equality of the temperature. At a depth of 500
fathoms the temperature of the water is already as low as 40° Fahr.,
and perfectly independent of the temperature of the surface-water; and
from the greatest depths upwards to about 1000 fathoms the temperature
is uniformly but a few degrees above freezing-point. Temperature,
therefore, ceases to offer an obstacle to the unlimited dispersal of
Deep-sea fishes.
4. The increased pressure by the water. The pressure of the atmosphere
on the level of the sea amounts to fifteen pounds per square inch of
the surface of the body of an animal; but the pressure amounts to a ton
weight for every 1000 fathoms of depth.
5. With the sunlight, vegetable life ceases in the depths of the sea.
All Deep-sea fishes are therefore carnivorous; the most voracious
feeding frequently on their own offspring, and the toothless kinds
being nourished by the animalcules which live on the bottom, or which,
“like a constant rain,” settle down from the upper strata towards the
bottom of the sea.
6. The perfect quiet of the water at great depths. The agitation of
the water, caused by the disturbances of the air, does not extend
beyond the depth of a few fathoms; below this surface-stratum there is
no other movement except the quiet flow of ocean-currents, and near
the bottom of the deep sea the water is probably in a state of almost
entire quiescence.
The effect upon fishes of the physical conditions described is
clearly testified by the modification of one or more parts of their
organisation, so that every Deep-sea fish may be recognised as such,
without the accompanying positive evidence that it has been caught
at a great depth; and _vice versa_, fishes reputed to have been
obtained at a great depth, and not having any of the characteristics
of the dwellers of the deep sea, must be regarded as surface-fishes.
The most striking characteristic, found in many Deep-sea fishes,
is in relation to the tremendous pressure under which they live.
Their osseous and muscular systems are, as compared with the same
parts of surface-fishes, very feebly developed. The bones have a
fibrous, fissured, and cavernous texture; are light, with scarcely
any calcareous matter, so that the point of a needle will readily
penetrate them without breaking. The bones, especially the vertebræ,
appear to be most loosely connected with one another; and it requires
the most careful handling to prevent the breaking of the connective
ligaments. The muscles, especially the great lateral muscles of the
trunk and tail, are thin, the fascicles being readily separated from
one another or torn, the connective tissue being extremely loose,
feeble, or apparently absent. This peculiarity has been observed
in the _Trachypteridæ_, _Plagyodus_, _Chiasmodus_, _Melanocetus_,
_Saccopharynx_. But we cannot assume that it actually obtains whilst
those fishes exist under their natural conditions. Some of them are
most rapacious creatures which must be able to execute rapid and
powerful movements to catch and overpower their prey; and for that
object their muscular system, thin as its layers may be, must be as
firm, and the chain of the segments of their vertebral column as firmly
linked together as in surface-fishes. Therefore, it is evident that the
change which the body of those fishes has undergone on their withdrawal
from the pressure under which they live is a much aggravated form of
the affection that is experienced by persons reaching great altitudes
in their ascent of a mountain or in a balloon. In every living organism
with an intestinal tract there are accumulations of free gases; and,
moreover, the blood and other fluids, which permeate every part of the
body, contain gases in solution. Under greatly diminished pressure
these gases expand, so that, if the withdrawal from a depth is not
an extremely slow and gradual process, the various tissues must be
distended, loosened, ruptured; and what is a vigorous fish at a depth
of 500 or more fathoms, appears at the surface as a loosely-jointed
body which, if the skin is not of sufficient toughness, can only be
kept together with difficulty. At great depths a fibrous osseous
structure and a thin layer of muscles suffices to obtain the same
results for which, at the surface, thickness of muscle and firm osseous
or cartilaginous tissue are necessary.
The muciferous system of many Deep-sea fishes is developed in an
extraordinary degree. We find already in fishes which are comparatively
little removed from the surface (that is to depths of 100–200 fathoms),
the lateral line much wider than in their congeners or nearest allies
which live on the surface, as in _Trachichthys_, _Hoplostethus_, many
_Scorpænidæ_. But in fishes inhabiting depths of 1000 and more fathoms,
the whole muciferous system is dilated; it is especially the surface of
the skull which is occupied by large cavities (_Macruridæ_, deep-sea
_Ophidiidæ_), and the whole body seems to be covered with a layer of
mucus. These cavities collapse and shrink in specimens which have been
preserved in spirit for some time, but a re-immersion in water for a
short time generally suffices to show the immense quantity of mucus
secreted by them. The physiological use of this secretion is unknown;
it has been observed to have phosphorescent properties in perfectly
fresh specimens.
The colours of Deep-sea fishes are extremely simple, their bodies
being either black or silvery; in a few only are some filaments or the
fin-rays of a bright scarlet colour. Among the black forms albinoes are
not scarce.
The organ of sight is the first to be affected by a sojourn in deep
water. Even in fishes which habitually live at a depth of only 80
fathoms, we find the eye of a proportionally larger size than in
their representatives at the surface. In such fishes the eyes increase
in size with the depth inhabited by them, down to the depth of 200
fathoms, the large eyes being necessary to collect as many rays of
light as possible. Beyond that depth small-eyed fishes as well as
large-eyed occur, the former having their want of vision compensated
for by tentacular organs of touch, whilst the latter have no such
accessory organs, and evidently see only by the aid of phosphorescence.
In the greatest depths blind fishes occur with rudimentary eyes and
without special organs of touch.
Many fishes of the deep sea are provided with more or less numerous,
round, shining, mother-of-pearl-coloured bodies, imbedded in the
skin. These so-called phosphorescent or luminous organs are either
larger bodies of an oval or irregularly elliptical shape placed on the
head, in the vicinity of the eye, or smaller round globular bodies
arranged symmetrically in series along the side of the body and tail,
especially near the abdominal profile, less frequently along the back.
The former have not yet been anatomically examined. The number of
pairs of the latter is in direct relation to that of the segments of
the vertebral column, the muscular system, etc. (meta*-meres); and
two kinds may be distinguished differing from each other in their
anatomical structure. The organs of one kind consist of an anterior,
biconvex, lens-like body, which is transparent during life, simple
or composed of rods (_Chauliodus_); and of a posterior chamber which
is filled with a transparent fluid, and coated with a dark membrane
composed of hexagonal cells, or of rods arranged as in a retina. This
structure is found in _Astronesthes_, _Stomias_, _Chauliodus_, etc. In
the other kind the organ shows throughout a simply glandular structure,
but apparently without an efferent duct (_Gonostoma_, _Scopelus_,
_Maurolicus_, _Argyropelecus_). Branches of the spinal nerves run to
each organ, and are distributed over the retina-like membrane or the
glandular follicles. The former kind of organs are considered by some
naturalists true organs of vision (accessory eyes), the function of the
latter being left unexplained by them.
Although, thus, these organs morphologically differ from each other,
there is no doubt that the functions of all have some relation to the
peculiar conditions of light under which the fishes provided with them
live; these fishes being either deep-sea forms or nocturnal pelagic
kinds. There are three possible hypotheses as to the function of these
organs:--
1. All the different kinds of organs are sensory, or, in other words,
accessory eyes.
2. Only the organs with a lenticular body are sensory, and those with a
glandular structure produce and emit phosphorescent light.
3. All are producers of light.
There are very serious objections to adopting the first view.
_Scopelus_ and _Argyropelecus_ possess not only perfectly developed,
but even large eyes, specially adapted for a nocturnal life; and
therefore accessory organs of vision must appear to be quite
superfluous to them. On the other hand, in Deep-sea fishes without
external eyes, which would seem to especially require these metameric
organs of sense, they are invariably absent. And, finally, it is
quite inconceivable that the glandular structures should have the
faculty of conveying impressions of light to the nervous centre.
The second supposition seems therefore to be nearer the truth; and
is supported by the fact that the glandular organs of Scopeli have
actually been observed to gleam with phosphorescent light, and by the
obvious morphological similarity of the organs with a lenticular body
and retina-like membrane to an organ of vision. We are, moreover,
justified, from an _à priori_ consideration, in supposing that in
depths to which no sunlight descends, and which are illuminated by
phosphorescent light only, peculiar organs of vision would have been
developed. On the other hand, this supposition is opposed by the fact
that many fishes which dwell in those abyssal depths are provided
with large ordinary eyes (as the _Trachypteri_, the majority of
_Macruridæ_), and, therefore, that the ordinary organ of vision is
quite sufficient for seeing by phosphorescent light. Thus, whilst we
must admit that those compound organs may prove to be organs of sense,
we maintain at the same time that their morphological nature is not
opposed to the belief that they too, like the glandular organs, are
producers of light. It may be produced at the bottom of the posterior
chamber, and emitted through the lenticular body in particular
directions, with the same effect as light is sent through the convex
glass of a “bull’s eye.” This hypothesis seems to be less bold than the
other, which would require us to believe that vertebrate animals, with
a nervous centre specialised for the reception of the impressions of
the higher senses, should receive them through the spinal chord.
[See _Ussow_, “Ueber den Bau der sogenannten
augenaehnlichen Flecken einiger Knochenfische.” St. Petersburg,
Bullet. 1879.]
Whenever we find in a fish long delicate filaments, developed in
connection with the fins or the extremity of the tail, we may
conclude that it is an inhabitant of still water and of quiet habits.
Many deep-sea fishes (_Trachypteridæ_, _Macruridæ_, _Ophidiidæ_,
_Bathypterois_) are provided with such filamentous prolongations, the
development of which is perfectly in accordance with their sojourn in
the absolutely quiet waters of abyssal depths.
Some of the raptatorial Deep-sea fishes have a stomach so distensible
and capacious that it can receive a fish of twice or thrice the bulk
of the destroyer (_Melanocetus_, _Chiasmodus_, _Saccopharynx_).
Deglutition is performed in them not by means of the muscles of the
pharynx, as in other fishes, but by the independent and alternate
action of the jaws, as in Snakes. These fishes cannot be said to
swallow their food, but rather draw themselves over their victim, in
the fashion of an _Actinia_.
Before the voyage of H.M.S. “Challenger,” scarcely thirty Deep-sea
fishes were known. This number is now much increased by the discovery
of many new species and genera; but, singularly, no new types of
families were discovered: nothing but what might have been expected
from our previous knowledge of this group of fishes. Modifications of
certain organs, perfectly novel, and of the greatest interest, were
found, as we shall see in the “Systematic Part;” but the most important
results of this voyage are that the general character of the abyssal
fish-fauna, the abundance of fishes, and the exact depths to which
fishes may descend, have been ascertained.
However, the statements of the depths at which the fishes collected by
the “Challenger” were taken cannot be received without some critical
examination of each individual species. No precaution was taken to
keep the mouth of the dredge closed during its descent or ascent, and
therefore it is quite within the limits of probability that sometimes
fishes were accidentally enclosed within the dredge, whilst it was
traversing the surface strata. And this has happened more than once;
for it is quite certain that common surface fishes like _Sternoptyx_
and _Astronestles_, never ranged to a depth of 2500 fathoms. On the
other hand, the majority of the fishes obtained offer sufficient
evidence from their own organisation that they live on the bottom, and
are unable to support themselves in the water at a certain distance
from the bottom or surface; and, consequently, that they actually were
obtained at the depth to which the dredge descended.
As far as the observations go at present, no distinct bathymetrical
regions, which would be characterised by peculiar forms, can be
defined. The depths from 200 to 600 fathoms are inhabited by
numerous forms, still strongly reminding us of surface types. To this
fauna belong the few Chondropterygians of the deep sea, a Sebastes
and Setarches, a Beryx and Polymixia, a Cottus, etc.; but they are
associated with many others which descend to the greatest depths.
And before anything like a division into bathymetrical zones can be
attempted, the observations of the “Challenger” expedition must be
confirmed and supplemented by other series of similar systematic
observations. One of the most startling conclusions at which we would
have to arrive from the “Challenger” observations is, that some of the
species of Deep-sea fishes would range from a depth of some 300 fathoms
down to one of 2000 fathoms; or, in other words, that a fish which
has once attained in its organisation to that modification by which
it is enabled to exist under the pressure of half a ton, can easily
accommodate itself to one of two tons or more,--a conclusion which is
not in accordance with anatomical facts, and which must be confirmed by
other observations before we can adopt it. But if the vertical range of
Deep-sea fishes is actually as it appears from the “Challenger” lists,
then there is no more distinct vertical than horizontal distribution of
Deep-sea fishes.
The greatest depth reached hitherto by a dredge in which fishes were
enclosed is 2900 fathoms. But the specimens thus obtained belong to a
species (_Gonostoma microdon_), which seems to be extremely abundant
in upper strata of the Atlantic and Pacific, and were therefore most
likely caught by the dredge in its ascent. The next greatest depth,
viz., 2750 fathoms, must be accepted as one at which fishes undoubtedly
do live; the fish obtained from this depth of the Atlantic, _Bathyophis
ferox_, showing by its whole habit that it is a form living on the
bottom of the ocean.
The fish-fauna of the deep sea is composed chiefly of forms or
modifications of forms which we find represented at the surface in the
cold and temperate zones, or which appear as nocturnal pelagic forms.
The Chondropterygians are few in number, not descending to a depth of
more than 600 fathoms. The Acanthopterygians, which form the majority
of the coast and surface faunas, are also scantily represented; genera
identical with surface types are confined to the same inconsiderable
depths as the Chondropterygians, whilst those Acanthopterygians which
are so much specialised for the life in the deep sea as to deserve
generic separation, range from 200 to 2400 fathoms. Three distinct
families of Acanthopterygians belong to the deep-sea fauna, viz.
_Trachypteridæ_, _Lophotidæ_, and _Notacanthidæ_; they respectively
consist of three, one, or two genera only.
_Gadidæ_, _Ophidiidæ_, and _Macruridæ_ are very numerous, ranging
through all depths; they constitute about one-fourth of the whole
deep-sea fauna.
Of _Physostomi_, the families of _Sternoptychidæ_, _Scopelidæ_,
_Stomiatidæ_, _Salmonidæ_, _Bathythrissidæ_, _Alepocephalidæ_,
_Halosauridæ_, and _Murænidæ_ are represented. Of these the
_Scopeloids_ are the most numerous, constituting nearly another fourth
of the fauna. _Salmonidæ_ are scarce, with three small genera only.
_Bathythrissidæ_ include one species only, which is probably confined
in its vertical as well as horizontal range; it occurs at a depth
of about 350 fathoms in the sea of Japan. The _Alepocephalidæ_ and
_Halosauridæ_, known before the “Challenger” expedition from isolated
examples only, prove to be true, widely-spread, deep-sea types. Eels
are well represented, and seem to descend to the greatest depths.
_Myxine_ has been obtained from a depth of 345 fathoms.
It will be useful to append a complete list of Deep-sea fishes, with
the depths as ascertained by the dredgings of the “Challenger:”--
_List of Deep-sea Fishes._
Fathoms.
CHONDROPTERYGIANS--
Raja 565
Scyllium 400
Centroscyllium 245
Centrophorus 345–500
ACANTHOPTERYGIANS--
Pomatomus (? down to) 200
Sebastes 275
Setarches 215
Beryx 345
Melamphaes (? beyond) 200
Polymixia 345
Nealotus
Nesiarchus
Aphanopus
Euoxymetopon
Lepidopus 345
Gempylus
Anomalops
? Antigonia
Diretmus
Cottus 565
Bathydraco 1260
Oneirodes
Melanocetus johnsonii 1850
„ bispinosus 360
Himantolophus
Chaunax 215
Ceratias 2400
Halieutichthys
Dibranchus 360
Trachypteridæ
Lophotes
Notacanthus rissoanus 1875
„ bonapartii 400
ANACANTHINI--
Melanonus 1975
Halargyreus
Lotella marginata 120–345
Physiculus 345
Uraleptus
Læmonema
Haloporphyrus australis 55–70
„ lepidion 345–600
„ rostratus 600–1375
Chiasmodus niger 1500
Sirembo grandis 1875
„ macrops 375
„ messieri 345
„ ocellatus 350
„ brachysoma 350
Acanthonus armatus 1075
Typhlonus nasus 2440
Aphyonus gelatinosus 1400
Rhinonus ater 2150
Bathynectes laticeps 2500
„ compressus 1075–2500
„ gracilis 1400
Pteridium
Macrurus (12 species) 120–700
Coryphænoides norvegicus
„ serratus
„ nasutus 345–565
„ villosus 345
„ rudis 500–650
„ æqualis 600
„ crassiceps 520–650
„ microlepis 215
„ murrayi 1100
„ serrulatus 700
„ filicauda 1800–2650
„ variabilis 1375–2425
„ affinis 1900
„ carinatus 500
„ longifilis 565
„ altipinnis 565–1875
„ asper 500–1875
„ leptolepis 350–2050
„ sclerorhynchus 1090
„ denticulatus 275–520
Malacocephalus 350
Bathygadus cottoides 520–700
„ multifilis 500
STERNOPTYCHIDÆ--
Argyropelecus 1127 [?]
Sternoptyx 0–2500 [?]
Polyipnus 255
Gonostoma denudatum
„ microdon 500–2900 [?]
„ elongatum 360–800
„ gracile 345–2425
Chauliodus 565–2560
SCOPELIDÆ--
Bathysaurus ferox 1100
„ mollis 1875–2385
Bathypterois longifilis 520–630
„ longipes 2650
„ quadrifilis 500–770
„ longicauda 2550
Chlorophthalmus agassizii 215
„ nigripinnis 120
„ gracilis 1100–1425
Scopelus engraulis 255
„ antarcticus 1950
„ mizolepis 800
„ dumerilii 215
„ macrolepidotus 520–630
„ crassiceps 675–1550
„ macrostoma 2350–2425
„ microps 1375
Odontostomus hyalinus
Odontostomus humeralis 500
Nannobrachium nigrum 500
Ipnops murrayi 1600–2150
Paralepis
Sudis
Plagyodus
STOMIATIDÆ--
Astronesthes niger 2500 [?]
Stomias boa 450–1800
„ barbatus
„ ferox
Echiostoma barbatum
„ micripnus 2150
„ microdon 2440
Malacosteus niger
„ indicus 500
Bathyophis ferox 2750
SALMONIDÆ--
Argentina
Microstoma
Bathylagus antarcticus 1950
„ atlanticus 2040
BATHYTHRISSIDÆ--
Bathythrissa dorsalis 345
ALEPOCEPHALIDÆ--
Alepocephalus rostratus
„ niger 1400
Platytroctes apus 1500
Bathytroctes microlepis 1090
„ rostratus 675
„ macrolepis 2150
Xenodermichthys 345
HALOSAURIDÆ--
Halosaurus owenii
„ affinis 565
„ macrochir 1090–1375
„ mediorostris 700
„ rostratus 2750
MURÆNIDÆ--
Nemichthys scolopacea
„ infans 500–2500
Cyema atrum 1500–1800
Saccopharynx
Synaphobranchus pinatus 345–1200
„ bathybius 1875–2050
„ brevidorsalis 1075–1375
„ affinis 345
Nettastoma parviceps 345
CYCLOSTOMATA--
Myxine australis 345
[Illustration: Fig. 111.--_Chiasmodus niger_; obtained in
the North Atlantic at a depth of 1500 fathoms; the specimen has
swallowed a large Scopelus (_s_); _o_, ventral fin.]
SYSTEMATIC AND DESCRIPTIVE PART.
The Class of Fishes is divided into four sub-classes:--
I. PALÆICHTHYES.--Heart with a contractile conus arteriosus;
intestine with a spiral valve; optic nerves non-decussating, or only
partially decussating.
II. TELEOSTEI.--Heart with a non-contractile bulbus arteriosus;
intestine without spiral valve; optic nerves decussating. Skeleton
ossified, with completely separated vertebræ.
III. CYCLOSTOMATA.--Heart without bulbus arteriosus; intestine
simple. Skeleton cartilaginous and notochordal. One nasal aperture
only. No jaws; mouth surrounded by a circular lip.
IV. LEPTOCARDII.--Heart replaced by pulsating sinuses; intestine
simple. Skeleton membrano-cartilaginous and notochordal. No skull; no
brain.
FIRST SUB-CLASS: PALÆICHTHYES.
_Heart with a contractile conus arteriosus;[30] intestine with a
spiral valve;[31] optic nerves non-decussating, or only partially
decussating;[32] skeleton cartilaginous or osseous._
This sub-class comprises the Sharks and Rays, and the Ganoid fishes.
Although based upon a singular concurrence of most important
characters, its members exhibit as great a diversity of form, and as
manifold modifications in the remainder of their organisation as the
_Teleostei_. The _Palæichthyes_ stand to the _Teleostei_ in the same
relation as the Marsupials to the Placentalia. Geologically, as a
sub-class, they were the predecessors of Teleosteous fishes; and it is
a remarkable fact that all those modifications which show an approach
of the ichthyic type to the Batrachians are found in this sub-class. We
divide it into two orders: _Chondropterygii_ and _Ganoidei_.
FIRST ORDER: CHONDROPTERYGII.
_Skeleton cartilaginous. Body with medial and paired fins, the
hinder pair abdominal. Vertebral column generally heterocercal, the
upper lobe of the caudal fin produced. Gills attached to the skin by
the outer margin, with several intervening gill-openings: rarely one
external gill-opening only. No gill-cover. No air-bladder. Two, three,
or more series of valves in the conus arteriosus. Ova large and few
in number,[33] impregnated and, in some species, developed within a
uterine cavity. Embryo with deciduous external gills.[34] Males with
intromittent organs attached to the ventral fins.[35]_
This order, for which, also, the name _Elasmobranchii_ has
been proposed (by Bonaparte), comprises the Sharks and Rays and
Chimæras, and is divided into two suborders: _Plagiostomata_ and
_Holocephala_.
FIRST SUB-ORDER: PLAGIOSTOMATA.
_From five to seven gill-openings. Skull with a suspensorium and the
palatal apparatus detached. Teeth numerous._
The Plagiostomes differ greatly among each other with regard to the
general form of their body: in the Sharks or _Selachoidei_ the
body is elongate, more or less cylindrical, gradually passing into the
tail; their gill-openings are lateral. In the Rays, or _Batoidei_,
the gill-openings are always placed on the abdominal aspect of the
fish; the body is depressed, and the trunk, which is surrounded by the
immensely developed pectoral fins, forms a broad flat disk, of which
the tail appears as a thin and slender appendage. Spiracles are always
present; the number of gill-openings is constantly five; no anal fin;
dorsal fins, if present, situated on the tail. However, some of the
Rays approach the Sharks in having the caudal portion less abruptly
contracted behind the trunk.
Fossil Plagiostomes are very numerous in all formations. Some of
the earliest determinable fish remains are believed to be, or are,
derived from Plagiostomes. Those which can be referred to any of
the following families will be mentioned subsequently: but there
are others, especially fin-spines, which leave us in doubt to which
group of Plagiostomes their owners had any affinity, thus _Onchus_
from the upper Silurian, continuing to carboniferous formations;
_Dimeracanthus_, _Homocanthus_, from the Devonian; _Oracanthus_,
_Gyracanthus_, _Tristychius_, _Astroptychius_, _Ptychacanthus_,
_Sphenacanthus_, etc., from carboniferous formations; _Leptacanthus_,
from the coal to the Oolite; _Cladacanthus_, _Cricacanthus_,
_Gyropristis_, and _Lepracanthus_, from the coal measures;
_Nemacanthus_, _Liacanthus_, from the Trias; _Astracanthus_,
_Myriacanthus_, _Pristacanthus_, from the Jurassic group.
A. SELACHOIDEI: SHARKS.
The elongate cylindrical body, generally terminating in a more or
less pointed snout, and passing into a powerful and flexible tail,
blade-like at its extremity, gives to the Sharks a most extraordinary
power of swimming, with regard to endurance as well as rapidity of
motion. Many, especially the larger kinds, inhabit the open ocean,
following ships for weeks, or pursuing shoals of fishes in their
periodical migrations. Other large-sized sharks frequent such parts
of the coast as offer them abundance of food; whilst the majority of
the smaller kinds are shore fishes, rarely leaving the bottom, and
sometimes congregating in immense numbers. The movements of sharks
resemble in some measure those of snakes, their flexible body being
bent in more than one curve when moving.
Sharks are most numerous in the seas between the Tropics, and become
scarcer beyond, a few only reaching the Arctic circle; it is not known
how far they advance southwards towards the Antarctic region. Some
species enter fresh waters, and ascend large rivers, like the Tigris
or Ganges, to a considerable distance. The pelagic as well as the
shore species have a wide geographical range. Very few descend to a
considerable depth, probably not exceeding 500 fathoms. There are about
140 different species known.
Sharks have no scales like those of other fishes; their integuments
are covered with calcified papillæ which, under the microscope, show a
structure similar to that of teeth. If the papillæ are small, pointed,
and close set, the skin is called “shagreen;” rarely they are larger,
appearing as bucklers or spines, of various sizes.
These fishes are exclusively carnivorous, and those armed with powerful
cutting teeth are the most formidable tyrants of the ocean. They have
been known to divide the body of a man in two at one bite, as if by
the sweep of a sword. Some of the largest sharks, however, which
are provided with very small teeth, are almost harmless, feeding on
small fishes only or marine invertebrates. Others, particularly of
the smaller kinds, commonly called “Dog-fishes,” have short or obtuse
teeth, and feed on shells or any other animal substance. Sharks scent
their food from a distance, being readily attracted by the smell of
blood or decomposing bodies.
In China and Japan, and many other eastern countries, the smaller kinds
of sharks are eaten. Sharks’ fins form in India and China a very
important article of trade, the Chinese preparing from them gelatine,
and using the better sorts for culinary purposes. The fins are obtained
not exclusively from Sharks but also from Rays, and assorted in two
kinds, viz. “white and black.” The white consist exclusively of the
dorsal fins, which are on both sides of the same uniform light colour,
and reputed to yield more gelatine than the other fins. The pectoral,
ventral, and anal fins pass under the denomination of black fins; the
caudal fin is not used. One of the principal places where shark fishery
is practised as a profession is Kurrachee. Dr. Buist, writing in 1850
(“Proc. Zool. Soc.” 1850, p. 100), states that there are thirteen
large boats, with crews of twelve men each, constantly employed in
this pursuit; that the value of the fins sent to the market varies
from 15,000 to 18,000 rupees; that one boat will sometimes capture at
a draught as many as one hundred sharks of various sizes; and that the
number total of sharks captured during the year amounts probably to not
less than 40,000. Large quantities are imported from the African coast
and the Arabian Gulf, and various ports on the coast of India. In the
year 1845–46, 8770 cwt. of sharks’ fins were exported from Bombay to
China.
FIRST FAMILY--CARCHARIIDÆ.
_Eye with a nictitating membrane. Mouth crescent-shaped, inferior.
Anal fin present. Two dorsal fins, the first opposite to the space
between pectoral and ventral fins, without spine in front._
CARCHARIAS.--Snout produced in the longitudinal axis of the
body; mouth armed with a series of large flat triangular teeth,
which have a smooth cutting or serrated edge. Spiracles absent.
A transverse pit on the back of the tail, at the root of the
caudal fin.
This genus comprises the true Sharks, common in the tropical, but less
so in the temperate seas. Between thirty and forty different species
have been distinguished, of which one of the most common is the “Blue
Shark” (_Carcharias glaucus_). Individuals of from twelve to fifteen
feet are of very common occurrence, but some of the species attain a
much larger size, and a length of 25 and more feet. Fishes of this
genus or of closely allied genera (_Corax_, _Hemipristis_) are not
uncommon in the chalk and tertiary formations.
GALEOCERDO.--Teeth large, flat, triangular, oblique, serrated
on both edges, with a deep notch on the outer margin. Spiracles
small. A pit on the tail, above and below, at the root of the
caudal fin. Two notches on the under caudal border, one of them
at the end of the spine.
[Illustration: Fig. 112.--Dentition of the Blue Shark (Carcharias
glaucus); the single teeth are of the natural size.]
Three species, of which one (_G. arcticus_) is confined to the
arctic and sub-arctic oceans. The others inhabit temperate and tropical
seas, and all attain to a very large size.
GALEUS.--Snout produced in the longitudinal axis of the
body; teeth equal in both jaws, rather small, flat, triangular,
oblique, serrated and with a notch. Spiracles small. No pit at
the commencement of the caudal fin, which has a single notch on
its lower margin.
These are small sharks, commonly called “Tope.” The species found on
the British coast is spread over nearly all the temperate and tropical
seas, and is common in California and Tasmania. It lives on the bottom,
and is very troublesome to fishermen by constantly taking away bait or
driving away the fishes which they desire to catch.
ZYGÆNA.--The anterior part of the head is broad, flattened, and
produced into a lobe on each side, the extremity of which is
occupied by the eye. Caudal fin with a single notch at its lower
margin. A pit at the root of the caudal fin. Spiracles none.
Nostrils situated on the front edge of the head.
The “Hammerheads,” or Hammerheaded Sharks, have a dentition very
similar to that of _Carcharias_, and although they do not attain to
the same large size, they belong to the most formidable fishes of
the ocean. The peculiar form of their head is quite unique among
fishes; young examples have the lateral extension of the skull much
less developed than adults. Five species are known, which are most
abundant in the tropics. By far the most common is _Zygæna malleus_,
which occurs in nearly all tropical and sub-tropical seas. Specimens
of this species may be often seen ascending from the clear blue depths
of the ocean like a great cloud. Cantor found in a female, nearly 11
feet long, thirty-seven embryons.--Hammerheads have lived from the
cretaceous epoch.
MUSTELUS.--The second dorsal fin is not much smaller than the
first. No pit at the root of the caudal, which is without
distinct lower lobe. Snout produced in the longitudinal axis
of the body. Spiracles small, behind the eyes. Teeth small,
numerous, similar in both jaws, obtuse, or with very indistinct
cusps, arranged like pavement.
The “Hounds” are small Sharks, abundant on the coasts of all the
temperate and tropical seas; two of the five species known occur on the
coasts of Europe, viz. _M. lævis_ and _M. vulgaris_. Closely allied as
these two species are, they yet show a most singular difference, viz.
that a placenta is developed in the uterus for the attachment of the
embryo in _M. lævis_ (the Γαλεὁς λεȋος of Aristotle, to whom this fact
was already known); whilst the embryons of _M. vulgaris_ are developed
without such placenta (see _J. Müller_, “Abhandl. Ak. Wiss.” Berl.
1840). The Hounds are bottom fish, which feed principally on shells,
crustaceans, and decomposing animal substances.
* * * * *
Several other genera belong to the family Carchariidæ, but it will
be sufficient to mention their names:--_Hemigaleus_, _Loxodon_,
_Thalassorhinus_, _Triænodon_, _Leptocarcharias_, and _Triacis_.
SECOND FAMILY--LAMNIDÆ.
_Eye without nictitating membrane. Anal fin present. Two dorsal fins;
the first opposite to the space between pectoral and ventral fins,
without spine in front. Nostrils not confluent with the mouth which is
inferior. Spiracles absent or minute._
All the fishes of this family attain to a very large size, and
are pelagic. But little is known of their reproduction. The first
appearance of this family is indicated by _Carcharopsis_, a genus from
carboniferous formations, the teeth of which differ from those of
_Carcharodon_ only by having a broad fold at the base. In the chalk and
tertiary formations almost all the existing genera are represented;
and, besides, _Oxytes_, _Sphenodus_, _Gomphodus_, and _Ancistrodon_,
which are known from teeth only, have been considered generically
distinct from the living Porbeagles.
LAMNA (OXYRHINA).--The second dorsal and anal are very small.
A pit at the root of the caudal, which has the lower lobe much
developed. Side of the tail with a prominent longitudinal keel.
Mouth wide. Teeth large, lanceolate, not serrated, sometimes
with additional basal cusps. On each side of the upper jaw, at
some distance from the symphysis, there is one or two teeth
conspicuously smaller than the others. Gill-openings very wide.
Spiracles minute.
[Illustration: Fig. 113.--Upper and lower tooth of Lamna.]
Of the “Porbeagles,” three species have been described, of which
the one occurring in the North Atlantic, and frequently straying to
the British coasts (_L. cornubica_), is best known. It attains to a
length of ten feet, and feeds chiefly on fishes; its lanceolate teeth
are not adapted for cutting, but rather for seizing and holding its
prey, which it appears to swallow whole. According to Pennant it is
viviparous; only two embryoes were found in the female which came under
his observation. Haast has found this species also off the coast of New
Zealand.
CARCHARODON.--The second dorsal and anal are very small. Pit at
the root of the caudal, which has the lower lobe well developed.
Side of the tail with a prominent longitudinal keel. Mouth wide.
Teeth large, flat, erect, regularly triangular, serrated. On
each side of the upper jaw, at some distance from the symphysis,
there is one or two teeth conspicuously smaller than the others.
Gill-openings wide.
One species only is known (_C. rondeletii_), which is the most
formidable of all Sharks. It is strictly pelagic; and appears to occur
in all tropical and sub-tropical seas. It is known to attain to a
length of 40 feet. The tooth figured here, of the natural size, is
taken from a jaw 20 inches wide in its transverse diameter (inside
measure), each half of the mandible measuring 22 inches.[36] The whole
length of the fish was 36½ feet.
Carcharodon teeth are of very common occurrence in various tertiary
strata, and have been referred to several species, affording ample
evidence that this type was much more numerously represented in that
geological epoch than in the recent fauna. Some individuals attained to
an immense size, as we may judge from teeth found in the Crag, which
are 4 inches wide at the base, and 5 inches long, measured along their
lateral margin. The naturalists of the “Challenger” expedition have
made the highly interesting discovery that teeth of similar size are
of common occurrence in the ooze of the Pacific, between Polynesia and
the west coast of America. As we have no record of living individuals
of that bulk having been observed, the gigantic species to which these
teeth belonged must have become extinct within a comparatively recent
period. Nothing is known of the anatomy, habits, and reproduction of
the surviving species, and no opportunity should be lost of obtaining
information on this Shark.
[Illustration: Fig. 114.--Tooth of Carcharodon rondeletii.]
ODONTASPIS.--The second dorsal and anal are not much smaller
than the first dorsal. No pit at the root of the caudal. Side of
the tail without keel. Mouth wide. Teeth large, awl-shaped, with
one or two small cusps at the base. Gill-openings of moderate
width.
Large Sharks from tropical and temperate seas; two species.
ALOPECIAS.--The second dorsal and anal very small. Caudal fin
of extraordinary length, with a pit at its root. No keel on the
side of the tail. Mouth and gill-openings of moderate width.
Teeth equal in both jaws, of moderate size, flat, triangular,
not serrated.
This genus consists of one species only, which is known by the name of
“Fox-shark” or “Thresher.” It is the most common of the larger kinds
of Sharks which occur on the British coasts; and seems to be equally
common in other parts of the Atlantic and Mediterranean, as well as on
the coasts of California and New Zealand. It attains to a length of
fifteen feet, of which the tail takes more than one half; and is quite
harmless to man. It follows the shoals of Herrings, Pilchards, and
Sprats in their migrations, destroying incredible numbers. When feeding
it uses the long tail in splashing the surface of the water, whilst it
swims in gradually decreasing circles round a shoal of fishes, which
are thus kept crowded together, falling an easy prey to their enemy.
Statements that it has been seen to attack Whales and other large
Cetaceans, rest upon erroneous observations.
SELACHE.--The second dorsal and anal very small. A pit at the
root of the caudal fin, which is provided with a lower lobe.
Side of the tail with a keel. Gill-openings extremely wide.
Teeth very small, numerous, conical, without serrature or
lateral cusps.
Also this genus consists of one species only, the “Basking Shark”
(Pélerin of the French). It is the largest Shark of the North Atlantic,
growing to a length of more than thirty feet. It is quite harmless if
not attacked; its food consisting of small fishes, and other small
marine animals swimming in shoals. On the west coast of Ireland it
is chased for the sake of the oil which is extracted from the liver,
one fish yielding from a ton to a ton and a-half. Its capture is not
unattended with danger, as one blow from the enormously strong tail is
sufficient to stave in the sides of a large boat. At certain seasons
it is gregarious, and many specimens may be seen in calm weather lying
together motionless, with the upper part of the back raised above the
surface of the water; a habit from which this Shark has derived its
name. The buccal and branchial cavities are of extraordinary width,
and, in consequence of the flabby condition of those parts, the head
presents a variable and singular appearance in specimens lying dead on
the ground. This peculiarity, as well as the circumstance that young
specimens have a much longer and more pointed snout than adult ones,
has led to the erroneous opinion that several different genera and
species of Basking Shark occur in the European seas. The branchial
arches of _Selache_ are provided with a very broad fringe of
long (five to six inches) and thin gill-rakers, possessing the same
microscopical structure as the teeth and dermal productions of Sharks.
Similar gill-rakers have been found in a fossil state in the Crag of
Anvers in Belgium, proving the existence of this Selachian type in the
tertiary epoch. Nothing is known of the reproduction of this fish.
The latest contributions to its history are by _Steenstrup_ in
“Overs. Dansk. Vidensk. Selsk., Forhandl.” 1873, and by _Pavesi_
in “Annal. Mus. Civ. Geneva,” 1874 and 1878.
THIRD FAMILY--RHINODONTIDÆ.
_No nictitating membrane. Anal fin present. Two dorsal fins, the
first nearly opposite to the ventrals, without spine in front. Mouth
and nostril near the extremity of the snout._
This small family comprises one species only, _Rhinodon typicus_,
a gigantic Shark, which is known to exceed a length of fifty feet,
but is stated to attain that of seventy. It does not appear to be
rare in the western parts of the Indian Ocean, and possibly occurs
also in the Pacific. It is one of the most interesting forms, not
unlike the Basking Shark of the Northern Seas, having gill-rakers like
that species; but very little is known of its structure and mode of
life. It is perfectly harmless, its teeth being extremely small and
numerous, placed in broad bands; it has been stated to feed on tang,
an observation which requires confirmation. The snout is very broad,
short, and flat; the eyes are very small. A pit at the root of the
caudal fin which has the lower lobe well developed; side of the tail
with a keel. A characteristic figure of this fish has been given by A.
Smith in his “Illustrations of the Zoology of South Africa,” Plate 26,
from a specimen which came ashore at the Cape of Good Hope.
[Illustration: Fig. 115.--Dentition of Notidanus indicus. _a_,
teeth in function; _b_, teeth in reserve; _u_, upper, and _l_,
lower, tooth, of natural size.]
FOURTH FAMILY--NOTIDANIDÆ.
_No nictitating membrane. One dorsal fin only, without spine,
opposite to the anal._
NOTIDANUS.--Dentition unequal in the jaws: in the upper jaw
one or two pairs of awl-shaped teeth, the following six being
broader, and provided with several cusps, one of which is much
the strongest. Lower jaw with six large comb-like teeth on each
side, beside the smaller posterior teeth. Spiracles small, on
the side of the neck. No pit at the root of the caudal fin.
Gill-openings wide, six in number in _Hexanchus_, seven in
_Heptanchus_.
Four species are known, distributed over nearly all the tropical and
sub-tropical seas; they attain to a length of about fifteen feet.
Fossil teeth belonging to this type have been found in Jurassic and
later formations (_Notidanus_ and _Aellopos_).
FIFTH FAMILY--SCYLLIIDÆ.
_Two dorsal fins, without spine: the first above or behind the
ventrals; anal fin present. No nictitating membrane. Spiracle always
distinct. Mouth inferior. Teeth small, several series generally being
in function._
SCYLLIUM.--The origin of the anal fin is always in advance of
that of the second dorsal. Nasal cavity separate from the mouth.
Teeth small, with a middle longer cusp, and generally one or two
small lateral cusps arranged in numerous series. Eggs similar to
those of the Rays (Fig. 79, p. 167).
The fishes of this genus are of small size, and commonly called
“Dog-fishes.” They are coast fishes, living on the bottom, and feeding
on Crustaceans, dead fishes, etc. None of the eight species known have
a very wide distribution, but where they occur they are generally
sufficiently abundant to prove troublesome to fishermen. They inhabit
most parts of the temperate and tropical seas. On the British coasts
two species are found, the “Larger” and “Lesser spotted Dog-fish,”
_Scyllium canicula_ and _Scyllium catulus_, which are said to be more
plentiful among the Orkney Islands than elsewhere. They are scarcely
ever brought to market; but the fishermen of some localities do not
disdain to eat them. Their flesh is remarkably white, a little
fibrous, and dry. In the Orkneys they are skinned, split up, cleaned,
and then spread out on the rocks to dry for home consumption. The skins
are used for smoothing down cabinet-work. It would be worth while to
apply the fins of these and other Sharks, which are so extensively
used in China for making gelatine soups, to the same purpose in this
country, or to dry them for exportation to the East. Most of the
species of Dog-fishes are spotted, and those of the allied genera,
_Parascyllium_ and _Chiloscyllium_, very handsomely ornamented.
Closely allied to _Scyllium_ is _Pristiurus_, from the coasts of
Europe, which is provided with a series of small flat spines on each
side of the upper edge of the caudal fin.
Fossil forms of Dog-fishes are not scarce in the Lias and Chalk:
_Scylliodus_, _Palæoscyllium_, _Thyellina_, _Pristiurus_.
GINGLYMOSTOMA.--The second dorsal fin opposite to, and somewhat
in advance of, the anal. Eyes very small; spiracle minute and
behind the eye. Nasal and buccal cavities confluent. The nasal
valves of both sides form one quadrangular flap in front of the
mouth, each being provided with a free cylindrical cirrhus. The
fourth and fifth gill-openings are close together. The teeth
stand either in many series, each having a strong median cusp
and one or two smaller ones on each side (_Ginglymostoma_), or
they stand in a few (three) series only, the foremost only being
in function, and each tooth having a convex, finely and equally
serrated margin (_Nebrius_).
Four species from the tropical parts of the Atlantic and Indian Oceans,
attaining to a length of some 12 feet. Pelagic.
STEGOSTOMA.--The first dorsal above the ventrals, the second in
advance of the anal, which is very close to the caudal. Tail,
with the caudal fin, exceedingly long, measuring one-half of the
total length. Eyes very small, spiracle as wide as, and situated
behind, the orbit. Nasal and buccal cavities confluent. Snout
very obtuse; upper lip very thick, like a pad, bent downwards
over the mouth, with a free cylindrical cirrhus on each side.
Teeth small, trilobed, in many series, occupying in both jaws
a transverse flat subquadrangular patch. The fourth and fifth
gill-openings are close together.
The single species (_St. tigrinum_) for which this genus has been
formed, is one of the commonest and handsomest sharks of the Indian
Ocean. Young individuals keep generally close to the coasts, whilst
the adult, which are from 10 to 15 feet long, are not rarely met in
the open ocean. The colour is a brownish yellow, ornamented with black
or brown transverse bands, or with snuff-coloured rounded spots; hence
this shark is frequently mentioned by the names of “Zebra-Shark” or
“Tiger-Shark.”
[Illustration: Fig. 116.--Chiloscyllium trispeculare, from
North-western Australia.]
CHILOSCYLLIUM.--The first dorsal fin above or behind the
ventrals. Anal fin placed far behind the second dorsal, and very
close to the caudal. Spiracle very distinct, below the eye.
Nasal and buccal cavities confluent. Nasal valve folded, with a
cirrhus. Teeth small, triangular, with or without lateral cusps.
The two last gill-openings close together.
“Dog-fishes,” from the Indian Ocean, of small size. Four species are
known, of which one, _Ch. indicum_, is one of the commonest
shore-fishes on the coasts of this region, extending from the southern
extremity of the African Continent to Japan.
[Illustration: Fig. 117.--Confluent nasal and buccal cavities of
the same fish.]
CROSSORHINUS.--The first dorsal behind the ventrals, the second
in advance of the anal, which is very close to the caudal. Tail
rather short. Eyes small. Spiracle a wide oblique slit, behind
and below the eye. Nasal and buccal cavities confluent. Head
broad, flat, with the snout very obtuse; mouth wide, nearly
anterior. A free nasal cirrhus; sides of the head with skinny
appendages. Anterior teeth rather large, long and slender,
without lateral lobes, the lateral tricuspid, smaller, forming
a few series only. The fourth and fifth gill-openings close
together.
Three species are known from the Australian and Japanese coasts. They
are evidently ground-sharks, which lie concealed on the bottom watching
for their prey. In accordance with this habit their colour closely
assimilates that of a rock or stone covered with short vegetable and
coralline growth--a resemblance increased by the frond-like tentacles
on the side of the head. This peculiarity of the integuments, which is
developed in a yet higher degree in Pediculati and Lophobranchs, is not
met with in any other Selachian. These Sharks grow to a length of 10
feet.
SIXTH FAMILY--HYBODONTIDÆ.
_Two dorsal fins, each with a serrated spine. Teeth rounded,
longitudinally striated, with one larger, and from two to four smaller
lateral cusps. Skin covered with shagreen._
Extinct. From carboniferous, liassic, and triassic formations. Several
genera have been distinguished; and if _Cladodus_ belongs to this
family, it would have been represented even in the Devonian.
[Illustration: Fig. 118.--Spine of Hybodus subcarinatus.]
SEVENTH FAMILY--CESTRACIONTIDÆ.
_No nictitating membrane. Two dorsal fins, the first opposite to
the space between pectoral and ventral fins; anal fin present. Nasal
and buccal cavities confluent. Teeth obtuse, several series being in
function._
[Illustration: Fig. 119.--Jaws of Port Jackson Shark, Cestracion
philippi.]
[Illustration: Fig. 120.--Upper jaw of the same, half natural
size.]
This family is one of particular interest, because representatives of
it occur in numerous modifications in primary and secondary strata.
Their dentition is uniformly adapted for the prehension and mastication
of crustaceous and hard-shelled animals. The fossil forms far exceeded
in size the species of the only surviving genus; they make, their
appearance with _Ctenoptychius_ in the Devonian; this is succeeded
in the coal-measures by _Psammodus_, _Chomatodus_, _Petrodus_,
_Coch__liodus_, _Polyrhizodus_, etc.; in the Trias and Chalk by
_Strophodus_, _Acrodus_, _Thectodus_, and _Ptychodus_. Of the 25 genera
known, 22 have lived in the periods preceding the Oolitic.
CESTRACION (HETERODONTUS).--Each dorsal fin armed with a spine
in front; the second in advance of the anal. Mouth rather
narrow. Spiracles small, below the posterior part of the eye.
Gill-openings rather narrow. Dentition similar in both jaws,
viz. small obtuse teeth in front, which in young individuals are
pointed and provided with from three to five cusps. The lateral
teeth are large, padlike, twice as broad as long, arranged in
oblique series, one series being formed by much larger teeth
than those in the other series.
[Illustration: Fig. 121.--Cochliodus contortus.]
[Illustration: Fig. 122.--Cestracion galeatus, Australia.]
Four species are known from Japan, Amboyna, Australia, the Galapagoes
Islands, and California; none exceed a length of 5 feet. The egg has
been figured on p. 168 (Fig. 80).
EIGHTH FAMILY--SPINACIDÆ.
_No membrana nictitans. Two dorsal fins; no anal. Mouth but slightly
arched; a long, deep, straight, oblique groove on each side of the
mouth. Spiracles present; gill-openings narrow. Pectoral fins not
notched at their origin._
The oldest representative of this family (_Palæospinax_) occurs at
Lyme Regis; its skin is granular; each dorsal fin possesses a spine;
the teeth in the jaws are dissimilar--the upper being multicuspid,
longitudinally ribbed as in Hybodus, the lower smooth and tricuspid.
_Drepanophorus_ and _Spinax primævus_ occur in Cretaceous formations of
England and the Lebanon.
CENTRINA.--Each dorsal fin with a strong spine. Trunk rather
elevated, trihedral, with a fold of the skin running along each
side of the belly. Teeth of the lower jaw erect, triangular,
finely serrated; those of the upper slender, conical, forming a
group in front of the jaw. Spiracles wide, behind the eye.
One species, _Centrina salviani_, from the Mediterranean and
neighbouring parts of the Atlantic; of small size.
ACANTHIAS.--Each dorsal fin with a spine. Teeth equal in both
jaws, rather small; their point is so much turned aside that
the inner margin of the tooth forms the cutting edge. Spiracles
rather wide, immediately behind the eye.
The two species of “Spiny Dog-fishes,” _A. vulgaris_ and _A.
blainvillii_, have a very remarkable distribution, being found in the
temperate seas of the Northern and Southern Hemispheres, but not in the
intermediate tropical zone. They are of small size, but occur at times
in incredible numbers, 20,000 having been taken in one scene on the
Cornish coast. They do much injury to the fishermen by cutting their
lines and carrying off their hooks.
CENTROPHORUS.--Each dorsal fin with a spine which, however, is
sometimes so small as to be hidden below the skin. Mouth wide.
Teeth of the lower jaw with the point more or less inclined
backwards and outwards. Upper teeth erect, triangular, or
narrow, lanceolate, with a single cusp. Spiracles wide, behind
the eye.
Eight species are known from the southern parts of the European seas,
and one from the Moluccas; they do not appear to exceed a length
of five feet. According to the observations of E. P. Wright, some
of the species at least live at a considerable depth, perhaps at a
greater depth than any of the other known Sharks. The Portuguese
fishermen fish for them in 400 or 500 fathoms with a line of some 600
fathoms in length. The Sharks caught were specimens of _Centrophorus
coelolepis_, from three to four feet long. “These sharks, as they
were hauled into the boat, fell down into it like so many dead pigs;
there was not the smallest motion of their bodies. There can be no
reasonable doubt that they were inhabitants of the same great depth as
_Hyalonema_” and that, in fact, they were killed by being dragged
to the surface from the pressure of water under which they lived.
The dermal productions of some of the species have a very peculiar
form, being leaf-shaped, pedunculate, or ribbed, or provided with an
impression.
SPINAX.--Each dorsal fin with a spine. Teeth of the lower jaw
with the point so much turned aside that the inner margin of
the tooth forms the cutting edge. Upper teeth erect, each with
a long-pointed cusp and one or two small ones on each side.
Spiracles wide, superior, behind the eye.
Three small species from the Atlantic and the southern extremity of
America. _Centroscyllium_ is an allied genus from the coast of
Greenland.
SCYMNUS.--Two short dorsal fins without spine, the first at a
considerable distance from the ventrals. Dermal productions
uniformly small. Nostrils at the extremity of the snout. Upper
teeth small, pointed; lower much larger, dilated, erect,
triangular, not very numerous. Spiracles wide.
A single species, _S. lichia_, is rather common in the Mediterranean
and the neighbouring parts of the Atlantic.
LÆMARGUS.--All the fins small; two dorsal fins, without spine,
the first at a considerable distance from the ventrals. Skin
uniformly covered with minute tubercles. Nostrils near the
extremity of the snout. The upper teeth small, narrow, conical;
the lower teeth numerous, in several series, the point so much
turned aside that the inner margin forms a cutting, non-serrated
edge. Jaws feeble. Spiracles of moderate width.
[Illustration: Fig. 123.--Dentition of the Greenland Shark. Some
teeth are represented of the natural size; those of the lower jaw
in three series.]
The “Greenland Shark” is an inhabitant of the Arctic regions, but
rarely straying to the latitudes of great Britain; it grows to a length
of about 15 feet, and, although it never or but rarely attacks man, is
one of the greatest enemies of the whale, which is often found with
large pieces bitten out of the tail by this Shark. Its voracity is so
great that, according to Scoresby, it is absolutely fearless of the
presence of man whilst engaged in feeding on the carcass of a whale,
so that it can be pierced through with a spear or knife without being
driven away. It is stated to be viviparous, and to produce about four
young at a birth.
[Illustration: Fig. 124.--Læmargus borealis, Greenland Shark.]
ECHINORHINUS.--Two very small dorsal fins, without spine, the
first opposite to the ventrals. Skin with scattered large round
tubercles. Nostrils midway between the mouth and the end of the
snout. Teeth equal in both jaws, very oblique, the point being
turned outwards; several strong denticulations on each side of
the principal point. Spiracles small.
The “Spinous Shark” is readily recognised by the short bulky form of
its body, short tail, and large spinous tubercles. It is evidently a
ground-shark, which probably lives at some depth and but accidentally
comes to the surface. More frequently met with in the Mediterranean, it
has been found several times on the south coast of England, and near
the Cape of Good Hope.
_Euprotomicrus_ and _Isistius_ are two other genera of this family;
they are pelagic and but little known.
NINTH FAMILY--RHINIDÆ.
_No anal fin; two dorsal fins. Spiracles present. Pectoral fins large,
with the basal portion prolonged forwards, but not grown to the head._
RHINA.--Head and body depressed, flat; mouth anterior.
Gill-openings rather wide, lateral, partly covered by the base
of the pectoral. Spiracles wide, behind the eyes. Teeth conical,
pointed, distant. Dorsal fins on the tail.
The “Angel-fish,” or “Monk-fish” (_Rh. squatina_), approaches the
Rays as regards general form and habits. Within the temperate and
tropical zones it is almost cosmopolitan, being well known on the
coasts of Europe, eastern North America, California, Japan, South
Australia, etc.; it does not seem to exceed a length of five feet; it
is viviparous, producing about twenty young at a birth.
Extinct forms, closely allied to the “Angel-fish,” are found in the
Oolite, and have been described as _Thaumas_. The carboniferous genus,
_Orthacanthus_, may have been allied to this family, but it was armed
with a spine immediately behind the head.
TENTH FAMILY--PRISTIOPHORIDÆ.
_The rostral cartilage is produced, into an exceedingly long, flat
lamina, armed along each edge with a series of teeth_ (saw).
These Sharks resemble so much the common Saw-fishes as to be easily
confounded with them, but their gill-openings are lateral, and not
inferior. They are also much smaller in size, and a pair of long
tentacles are inserted at the lower side of the saw. The four species
known (_Pristiophorus_) occur in the Australian and Japanese seas.
_Squaloraja_, from the Lias, is supposed to have its nearest
affinities to this family.
B. BATOIDEI--RAYS.
In the typical Rays the body is excessively depressed, and forms, with
the expanded pectoral fins, a circular or sub-rhomboidal disk, of which
the slender tail appears as a more or less long appendage. In the two
families which we shall place first (_Pristidæ_ and _Rhinobatidæ_),
the general habit of the body still resembles that of the Sharks,
but the gill-openings are ventral, as in the true Rays; the anal fin
is invariably absent, and the dorsal fins, if developed, are placed
on the tail. The mode of life of those fishes is quite in accordance
with the form of their body. Whilst the species with a shark-like body
and muscular tail swim freely through the water, and are capable of
executing rapid and sustained motions, the true Rays lead a sedentary
life, moving slowly on the bottom, rarely ascending to the surface.
Their tail has almost entirely lost the function of an organ of
locomotion, acting in some merely as a rudder. They progress solely by
means of the pectoral fins, the broad and thin margins of which are set
in an undulating motion, entirely identical with that of the dorsal and
anal fins of the _Pleuronectidæ_. They are exclusively carnivorous,
like the Sharks, but unable to pursue and catch rapidly-moving
animals; therefore they feed chiefly on molluscous and crustaceous
animals. However, the colour of their integuments assimilates so
closely that of their surroundings, that other fishes approach them
near enough to be captured by them. The mouth of Rays being entirely
at the lower surface of the head, the prey is not directly seized with
the jaws; but the fish darts over its victim so as to cover and hold it
down with its body, when it is conveyed by some rapid motions to the
mouth.
Rays do not descend to the same depth as Sharks; with one
exception,[37] at least, none have been known to have been caught by a
dredge worked in more than 100 fathoms. The majority are coast fishes,
and have a comparatively limited geographical range, none extending
from the northern temperate zone into the southern. However, some,
if not all the species of the family _Myliobatidæ_, which includes
the giants of this division of Plagiostomes, have a claim of being
included among the Pelagic fishes, as they are frequently met with
in the open ocean at a great distance from the shore. It is probable
that the occurrence of such individuals in the open sea indicates the
neighbourhood of some bank or other comparatively shallow locality.
Many species are exclusively confined to fresh water, and occur far
inland, especially in tropical America.
The majority are oviparous. All have five pairs of gill-openings. The
number of known species is about the same as that of Sharks, viz. 140.
FIRST FAMILY--PRISTIDÆ.
_The snout is produced into an exceedingly long flat lamina, armed
with a series of strong teeth along each edge_ (saw).
PRISTIS.--Body depressed and elongate, gradually passing into
the strong and muscular tail. Pectoral fins, with the front
margins quite free, not extending to the head. No tentacles
below the saw. Teeth in the jaws minute, obtuse. Dorsal fins
without spine, the first opposite or close to the base of the
ventrals.
“Saw-fishes.” Abundant in tropical, less so in sub-tropical seas. They
attain to a considerable size, specimens with a saw 6 feet long and 1
foot broad at the base not being of uncommon occurrence. The saw, which
is their weapon of attack, renders them most dangerous to almost all
the other large inhabitants of the ocean. Its endoskeleton consists
of three, sometimes five, rarely four, hollow cylindrical tubes,
placed side by side, tapering towards the end, and incrusted with an
osseous deposit. These tubes are the rostral processes of the cranial
cartilage, and exist in all Rays, though in them they are shorter and
much less developed. The teeth of the saw are implanted in deep sockets
of the hardened integument. The teeth proper, with which the jaws
are armed, are much too small for inflicting wounds or seizing other
animals. Saw-fishes use this weapon in tearing pieces of flesh off
an animal’s body or ripping open its abdomen. The detached fragments
or protruding soft parts are then seized by them and swallowed. Five
distinct species of Saw-fishes are known.
Saws of extinct species have been found in the London clay of Sheppey
and in the Bagshot sands.
SECOND FAMILY--RHINOBATIDÆ.
_Tail strong and long, with two well-developed dorsal fins, and a
longitudinal fold on each side; caudal developed. Disk not excessively
dilated, the rayed portion of the pectoral fins not being continued to
the snout._
RHYNCHOBATUS.--Dorsal fins without spine, the first opposite to
the ventrals. Caudal fin with the lower lobe well developed.
Teeth obtuse, granular, the dental surfaces of the jaws being
undulated.
[Illustration: Fig. 125.--Dentition of _Rhynchobatus_.]
Two species, _Rh. ancylostomus_ and _Rh. djeddensis_, are very common
on the tropical coasts of the Indian Ocean. They feed on hard-shelled
animals, and attain scarcely a length of 8 feet.
RHINOBATUS.--Cranial cartilage produced into a long rostral
process, the space between the process and pectoral fin
being filled by a membrane. Teeth obtuse, with an indistinct
transverse ridge. Dorsal fins without spine, both at a great
distance behind the ventral fins. Caudal fin without lower lobe.
Numerous on the coasts of tropical and sub-tropical seas; about twelve
species. _Trygonorhina_ is an allied genus from South Australia.
The oolitic genus _Spathobatis_ is scarcely distinct from
_Rhinobatus_; and another fossil from Mount Lebanon has been
actually referred to this latter genus. _Trigorhina_ from Monte
Postale must be placed here.
THIRD FAMILY--TORPEDINIDÆ.
_The trunk is a broad, smooth disk. Tail with a longitudinal fold
on each side; a rayed dorsal fin is generally, and a caudal always,
present. Anterior nasal valves confluent into a quadrangular lobe.
An electric organ composed of vertical hexagonal prisms between the
pectoral fins and the head._
“Electric Rays.” The electric organs with which these fishes are armed
are large, flat, uniform bodies, lying one on each side of the head,
bounded behind by the scapular arch, and laterally by the anterior
crescentic tips of the pectoral fins. They consist of an assemblage
of vertical hexagonal prisms, whose ends are in contact with the
integuments above and below; and each prism is subdivided by delicate
transverse septa, forming cells, filled with a clear, trembling,
jelly-like fluid, and lined within by an epithelium of nucleated
corpuscles. Between this epithelium and the transverse septa and walls
of the prism there is a layer of tissue on which the terminations
of the nerves and vessels ramify. Hunter counted 470 prisms in each
battery of _Torpedo marmorata_, and demonstrated the enormous
supply of nervous matter which they receive. Each organ receives one
branch of the Trigeminal nerve and four branches of the Vagus, the
former, and the three anterior branches of the latter, being each as
thick as the spinal chord (electric lobes). The fish gives the electric
shock voluntarily, when it is excited to do so in self-defence or
intends to stun or to kill its prey; but to receive the shock the
object must complete the galvanic circuit by communicating with the
fish at two distinct points, either directly or through the medium
of some conducting body. If an insulated frog’s leg touches the fish
by the end of the nerve only, no muscular contractions ensue on the
discharge of the battery, but a second point of contact immediately
produces them. It is said that a painful sensation may be produced
by a discharge conveyed through the medium of a stream of water. The
electric currents created in these fishes exercise all the other known
powers of electricity: they render the needle magnetic, decompose
chemical compounds, and emit the spark. The dorsal surface of the
electric organ is positive, the ventral surface negative.
[The literature on the electric organ of Torpedo is very
extensive. Here may be mentioned _Lorenzini_, “Osservazioni
intorno alle Torpedini,” (1678); _Walsh_, “On the Electric
Property of the Torpedo,” in Philos. Trans., 1773; _Hunter_,
“Anatomical Observations on the Torpedo,” _ibid._;
_Davy_, “Observations on the Torpedo,” in Philos. Trans.,
1834; _Matteucci_ and _Savi_, “Traité des Phénomènes
Electro-Physiologiques,” 1844.]
Of the genus _Torpedo_ six species are known, distributed over the
Atlantic and Indian Oceans; three of them are rather common in the
Mediterranean, and one (_T. hebetans_) reaches the south coast of
England. They attain to a width of from two to three feet, and
specimens of that size are able to disable by a single discharge a
full-grown man, and, therefore, may prove dangerous to bathing persons.
Other genera, differing from _Torpedo_ in the position and structure of
some of the fins, are found in other tropical and sub-tropical seas,
viz. _Narcine_, _Hypnos_, _Discopyge_ (Peru), _Astrape_, and _Temera_.
All, like electric fishes generally, have a naked body.
A large fish, of the general appearance of a Torpedo, has been found at
Monte Bolca; and _Cyclobatis_, from the upper cretaceous limestone of
Lebanon, is probably another extinct representative of this family.
FOURTH FAMILY--RAJIDÆ.
_Disk broad, rhombic, generally with asperities or spines; tail with
a longitudinal fold on each side. The pectoral fins extend to the
snout. No electric organ; no serrated caudal spine._
RAJA.--Two dorsal fins on the tail, without spine; tail with
a rudimentary caudal fin, or without caudal. Each ventral fin
divided into two by a deep notch. Teeth small, obtuse, or
pointed. Pectoral fins not extending forwards to the extremity
of the snout. Nasal valves separated in the middle, where they
are without a free margin (see Fig. 1, p. 34).
[Illustration: Fig. 126.--Raja lemprieri, from Tasmania.]
[Illustration: Fig. 127.--Dermal spines of a male Thornback, Raja
clavata.]
Of all the genera of _Batoidei_, Rays have the widest geographical
range; they are chiefly inhabitants of temperate seas, and much more
numerous in those of the Northern than of the Southern Hemisphere.
They advance more closely to the Arctic and Antarctic circles than
any other member of this group. More than thirty species are known,
of which the following are found on the British coast:--The Thornback
(_R. clavata_), the Homelyn Ray (_R. maculata_), the Starry Ray (_R.
radiata_), the Sandy Ray (_R. circularis_), the common Skate (_R.
batis_), the Burton Skate (_R. marginata_), and the Shagreen Skate (_R.
fullonica_). Some of these species, especially the Skates, attain a
considerable size, the disk measuring six and even seven feet across.
All are eatable, and some of them regularly brought to market. In the
majority of the species peculiar sexual differences have been observed.
In some, as in the Thornback, all or some of the teeth are pointed
in the male sex, whilst they are obtuse and flat in the female. The
males of all are armed with patches of claw-like spines, retractile in
grooves of the integument, and serially arranged occupying a space on
the upper side of the pectoral fin near the angle of the disk, and
frequently also the sides of the head. In species which are armed with
bucklers or asperities it is the female which is principally provided
with these dermal productions, the male being entirely or nearly
smooth. Also the colour is frequently different in the two sexes.
Other genera of this family are _Psammobatis_, _Sympterygia_, and
_Platyrhina_. Although probably this family was well represented in
cretaceous and tertiary formations, the remains found hitherto are
comparatively few. _Arthropterus_, from the Lias, seems to have been a
true Ray; and dermal spines of a species allied to the Thornback (_Raja
antiqua_) are abundant in the crag deposits of Suffolk and Norfolk.
FIFTH FAMILY--TRYGONIDÆ.
_The pectoral fins are uninterruptedly continued to, and confluent
at, the extremity of the snout. Tail long and slender, without lateral
longitudinal folds; vertical fins none, or imperfectly developed, often
replaced by a strong serrated spine._
The “Sting-Rays” are as numerous as the Rays proper, but they inhabit
rather tropical than temperate seas. The species armed with a spine
use it as a weapon of defence, and the wounds inflicted by it are, to
man, extremely painful, and have frequently occasioned the loss of a
limb. We have mentioned above (p. 190) that the danger arises from the
lacerated nature of the wound as well as from the poisonous property of
the mucus inoculated. The spines (Fig. 98, p. 190) are always barbed on
the sides, and may be eight or nine inches long in the larger species.
They are shed from time to time, and replaced by others growing behind
the one in function, as the teeth of the fishes of this order, or as
the fangs of a poisonous snake. Fossil species of _Trygon_ and
_Urolophus_ occur in the tertiary strata of Monte Bolca and Monte
Postale. The genera into which the various species have been divided
are the following:--
UROGYMNUS.--Tail long, without fin or spine, sometimes with a
narrow cutaneous fold below. Body densely covered with osseous
tubercles. Teeth flattened.
Only one species is known (_U. asperrimus_), common in the Indian
Ocean, and with a body from 4 to 5 feet long; the skin is frequently
used for covering shields and the handles of swords and other weapons,
its rough surface offering a firm hold to the hand.
TRYGON.--Tail very long, tapering, armed with a long
arrow-shaped barbed spine. Body smooth or with tubercles. Nasal
valves coalescent into a quadrangular flap. Teeth flattened.
Some twenty-five species are known, one of which (_T. pastinaca_)
extends from the south coast of England and the east coast of North
America through the Atlantic and Indian Ocean to Japan. The majority
of the species belong to the tropical parts of the Indian and Atlantic
Oceans; some inhabit exclusively freshwaters of eastern tropical
America. A closely allied genus is _Tæniura_, with six species.
UROLOPHUS.--Tail of moderate length, with a distinct rayed
terminal fin, armed with a barbed spine, without or with a
rudimentary dorsal fin. Teeth flattened.
Seven species from tropical seas, apparently of small size.
[Illustration: Fig. 128.--Urolophus cruciatus, from Australia.]
PTEROPLATEA.--Body at least twice as broad as long; tail very
short and thin, without or with a rudimentary fin, and with a
serrated spine. Teeth very small, uni- or tri-cuspid.
Six species from temperate and tropical seas.
SIXTH FAMILY--MYLIOBATIDÆ.
_The disk is very broad, in consequence of the great development of
the pectoral fins, which, however, leave the sides of the head free,
and reappear at the extremity of the snout as a pair of detached
(cephalic) fins. Viviparous._
“Devil-fishes,” “Sea-devils,” or “Eagle-rays.” Generally of large
size, inhabiting temperate and tropical seas. Some genera possess a
pair of singular cephalic processes, which generally project in a
direction parallel to the longitudinal axis of the body, but are said
to be flexible in the living fish, and used for scooping food from the
bottom and conveying it to the mouth. In all the species the dentition
consists of perfectly flat molars, forming a kind of mosaic pavement in
both the upper and lower jaws: a most perfect mechanical arrangement
for crushing alimentary substances.
[Illustration: Fig. 129.--Jaws of an Eagle-Ray, _Myliobatis
aquila._]
MYLIOBATIS.--Teeth sexangular, large, flat, tessellated, those
in the middle much broader than long; several narrower series
on each side. Tail very long and thin, with a dorsal fin near
its root; generally a serrated spine behind the fin.
Seven species are known, two of which are European, one (_M. aquila_)
being almost cosmopolitan, and occasionally found on the British coast.
The young differ much from the adult, having no median series of larger
teeth, but all the teeth of equal size and regularly sexangular. Also
the tail is much longer in young examples than in old ones, and the
coloration more ornamental. Teeth of species very closely allied to, or
perhaps even identical with, existing species, are found in tertiary
formations.
AËTOBATIS.--Form of the head, body, and tail as _Myliobatis_.
The nasal valves remain separate, each forming a long flap.
The lower dental lamina projects beyond the upper. Teeth flat,
broad, forming a single series, equivalent to the median series
of _Myliobatis_, there being no small lateral teeth.
[Illustration: Fig. 130.--Aëtobatis narinari.]
One species only (_A. narinari_) which is found in almost all tropical
seas, and of exceedingly common occurrence in the Atlantic and Indian
Oceans; it does not seem to grow to a very large size (perhaps not
exceeding 5 feet in width), and is readily recognised by numerous round
bluish-white spots, with which the back is ornamented. Fossils of this
genus occur in the English Eocenes and the Swiss Molasse.
[Illustration: Fig. 131.--Aëtobatis subarcuatus, from
Bracklesham.]
RHINOPTERA.--The cephalic appendages are bent inwards, and situated
at the lower side of the snout. Nasal valves confluent into a broad
flap, with free margin. Teeth broad, flat, tessellated, in five or
more series, the middle being the broadest, and the others decreasing
in width outwards. Tail very slender, with a dorsal fin before the
serrated spine.
[Illustration: Fig. 132.--Rhinoptera woodwardi; fossil.]
[Illustration: Fig. 133.--Rhinoptera polyodon.]
Seven species from tropical and sub-tropical seas are known; of
_Rhinoptera polyodon_ nothing is known except the jaws; and as its
dentition is very peculiar, no opportunity should be lost of obtaining
and preserving entire animals. Teeth very similar to those of existing
species, and described as _Zygobatis_, occur in the Norwich Crag
and in Miocene formations of Switzerland.
DICEROBATIS (CEPHALOPTERA).--Cephalic appendages pointing
straight forwards or inwards. Nostrils widely separated from
each other. Mouth inferior, wide. Both jaws with very numerous
and very small flat or tubercular teeth. Tail very slender,
with a dorsal fin between the ventrals, and with or without a
serrated spine.
CERATOPTERA.--Cephalic appendages pointing forwards or inwards.
Mouth anterior; wide. Teeth in the lower jaw only, very small.
Tail very slender, with a dorsal fin between the ventrals and
without spine.
[Illustration: Fig. 134.--Dicerobatis draco, from Misol.]
The species of these two last genera are not yet well distinguished;
about five of _Dicerobatis_ and two of _Ceratoptera_ are known from
tropical and temperate seas, but their occurrence in the latter is
rather sporadic. Some of them, if not all, attain an enormous size.
One mentioned by Risso, taken off Messina, weighed 1250 pounds.
Several observers speak of having seen them in pairs, the male being
usually the smaller. Of a pair mentioned by Risso the female was first
taken, and the male remained hovering about the boat for three days,
and was afterwards found floating dead on the surface. Still larger
individuals, but of uncertain species, are mentioned by Lacépède, who
says that one taken at Barbadoes required seven yoke of oxen to draw
it. A sketch of another, which was said to be twenty feet long, was
sent to Lacépède; and Sonnini speaks of one which appeared to him to be
longer and wider than the ship in which he was sailing. A fœtus taken
from the uterus of the mother captured at Jamaica, and preserved in
the British Museum, is five feet broad, and weighed twenty pounds. The
mother measured fifteen feet in width as well as in length, and was
between three and four feet thick. The capture of “Devil-fishes” of
such large size is attended with danger, as they not rarely attack and
capsize the boat. They are said to be especially dangerous when they
accompany their young, of which they bring forth one only at a time.
SECOND SUB-ORDER--HOLOCEPHALA.
_One external gill-opening only, covered by a fold of the skin, which
encloses a rudimentary cartilaginous gill-cover; four branchial clefts
within the gill-cavity. The maxillary and palatal apparatus coalescent
with the skull._
This suborder is represented in the living fauna by one family only,
_Chimæridæ_; it forms a passage to the following order of fishes, the
Ganoids. In external appearance, and with regard to the structure of
their organs of propagation, the Chimæras are Sharks (See Fig. 96, p.
184). The males are provided with “claspers” in connection with the
ventral fins, and the ova are large, encased in a horny capsule, and
few in number; and there is no doubt that they are impregnated within
the oviduct, as in Sharks. Chimæras are naked, but, as in _Scylliidæ_,
very young individuals possess a series of small “placoid” spines,
which occupy the median line of the back, and remind us of similar
dermal productions in the Rays. The males, besides, are provided with
a singular erectile appendage, spiny at its extremity, and received
in a groove on the top of the head. On the other hand, the relations
of the Chimæras to the Ganoid, and, more especially, Dipnoous type
become manifest in their notochordal skeleton and continuity of
cranial cartilage. The spine in front of the first dorsal fin is
articulated to the neural apophysis, and not merely implanted in the
soft parts, and immovable as in Sharks. A cartilaginous operculum
makes its appearance, and the external gill-opening is single. The
dentition is that of a Dipnoid, each “jaw” being armed with a pair of
broad dental plates, with the addition of a pair of smaller cutting
teeth in the upper “jaw.” Fossils of similar dental combination are
not rare in strata, commencing from the Lias and the bottom of the
Oolitic series; but it is impossible to decide in every case whether
the fossil should be referred to the Holocephalous or Dipnoous type.
According to Newberry, Chimæroid fishes commence in the Devonian with
_Rhynchodus_, the remains of which were discovered by him in Devonian
rocks of Ohio. Undoubted Chimæroids are _Elasmodus_, _Psaliodus_,
_Ganodus_, _Ischyodus_, _Edaphodon_, and _Elasmognathus_, principally
from mesozoic and tertiary formations. Very similar fossils occur
in the corresponding strata of North America. A single species of
_Callorhynchus_ has been discovered by H. Hector in the Lower Greensand
of New Zealand.
The living Chimæras are few in number, and remain within very moderate
dimensions, probably not exceeding a length of five feet, inclusive
of their long filamentous, diphycercal tail. They are referred to two
genera.
CHIMÆRA.--Snout soft, prominent, without appendage. The dorsal
fins occupying the greater part of the back, anterior with
a very strong and long spine. Longitudinal axis of the tail
nearly the same as that of the trunk, its extremity being
provided with a low fin above and below, similar in form to a
dorsal and anal fin. Anal fin very low.
Three species are known: _Ch. monstrosa_, from the coasts of Europe and
Japan and the Cape of Good Hope; _Ch. colliei_ from the west coast of
North America; and _Ch. affinis_ from the coast of Portugal. (See Fig.
96, p. 184.)
CALLORHYNCHUS.--Snout with a cartilaginous prominence,
terminating in a cutaneous flap. Two dorsal fins, the anterior
with a very strong and long spine. Extremity of the tail
distinctly turned upwards, with a fin along its lower edge, but
without one above. Anal fin close to the caudal, short and deep.
One species (_C. antarcticus_) is common in the Southern temperate
zone. Cunningham describes the egg (see Fig. 81, p. 169), as being of
a dark greenish-black colour, and, in general, measuring from eight
to nine or even ten inches in length, by about three in breadth. It
consists of a central, somewhat spindle-shaped convex area (between
the horny walls of which the young fish lies), surrounded by a broad
plicated margin, which is fringed at the edge, and covered on the under
surface with fine light brownish-yellow hairs.
SECOND ORDER--GANOIDEI.
_Skeleton cartilaginous or ossified. Body with medial and paired
fins, the hinder pair abdominal. Gills free, rarely partially attached
to the walls of the gill-cavity. One external gill-opening only on
each side; a gill-cover. Air-bladder with a pneumatic duct. Ova small,
impregnated after exclusion. Embryo sometimes with external gills._
To this order belong the majority of the fossil fish remains of
palæozoic and mesozoic age, whilst it is very scantily represented
in the recent fauna, and evidently verging towards total extinction.
The knowledge of the fossil forms, based on mere fragments of the
hard parts of the body only, is very incomplete, and therefore their
classification is in a most unsatisfactory state. In the following
pages only the most important groups will be mentioned.
[For a study of details we have to refer to _Agassiz_, “Poissons
Fossiles;” _Owen_, “Palæontology,” Edinb. 1861, 8vo; _Huxley_,
“Preliminary Essay upon the Systematic Arrangement of the Fishes
of the Devonian Epoch,” in Mem. Geolog. Survey, Dec. 10; Lond.
1861, and “Illustrations of the Structure of Crossopterygian
Ganoids,” _ibid._ December 12, 1866; _Traquair_, “The Ganoids of
the British Carboniferous Formations,” part I. “Palæoniscidæ.”
Palæontogr. Soc. Lond. 1877.]
Eight suborders may be distinguished at present.
FIRST SUB-ORDER--PLACODERMI.
_Extinct. The head and pectoral region of the body encased in great
bony, sculptured plates, with dots of enamel; the remainder of the body
naked, or with ganoid scales; skeleton notochordal._
Comprises the oldest vertebrate remains, from Devonian and
Carboniferous formations. _Pterichthys_: (Figs. 135 and 136), tail
tapering, covered with small ganoid scales, without caudal fin; the
cephalic shield was probably moveably joined to the cuirass of the
trunk, and both were composed of several pieces; the abdominal shield
consisted of one single median plate, and two pairs of lateral plates,
a third small pair being sometimes observed detached in front of the
anterior pair; pectoral exceedingly long, consisting of two pieces
movably connected with each other; tail scaly, and short; a small
dorsal fin placed on the tail; a pair of small ventrals; jaws small,
with confluent denticles. Several species have been distinguished
in remains found in the strata of Caithness and other localities in
Scotland. _Coccosteus_ (Fig. 137, p. 354): all the bony plates are
firmly united, no pectoral spines; tail naked and long; a dorsal and
anal fin supported by interneural and interhæmal spines. Dentition
unknown. _Dinichthys_: a gigantic fish from the Devonian of North
America (estimated at from 15 to 18 feet in length), with the dermal
covering very similar to that of Coccosteus, but with a simple arched
dorsal shield. As in this latter genus the caudal extremity does not
possess external or internal bony parts, and the ventral plastron
of both genera corresponds in every particular; the dentition is so
singularly like that of Lepidosiren, that Newberry (Geolog. Survey of
Ohio, vol. ii. part 2) considers this genus to be in genetic relation
to the Dipnoi. The following genera have been united in a separate
family, _Cephalaspidæ_; viz. _Cephal__aspis_: head covered by a
continuous shield with tubercular surface, produced into a horn at each
posterior corner; a median dorsal backward prolongation bears a spine;
heterocercal. _Auchenaspis_ and _Didymaspis_: allied to the preceding,
but with the cephalic shield divided into a larger anterior and smaller
posterior piece. _Pteraspis_: with the cephalic shield finely striated
or grooved, composed of seven pieces. _Scaphaspis_ and _Cyathaspis_:
with the surface of the head-shield similarly sculptured as in
_Pteraspis_, but simple in the former, and composed of four pieces in
the latter. _Astrolepis_: attained to the gigantic size of between
twenty and thirty feet; its mouth was furnished with two rows of teeth,
of which the outer ones were small, the inner much larger.
[See Ray Lankester, A. Monograph of the Fishes of the Old Red
Sandstone of Britain. Part I. Cephalaspidæ. Lond. 1868 and 1870.
4to.]
[Illustration: Fig. 135.--Dorsal surface of Pterichthys, after
Pander. _d_, Dorsal fin; _c_, pectoral member; 2–10,
head-bucklers; 11–13, dorsal bucklers.]
[Illustration: Fig. 136.--Ventral aspect of Pterichthys, after
Pander. 15, mandible (?); 16–21, ventral bucklers.]
[Illustration: Fig. 137.--Coccosteus, after Pander. _A_, Anal
fin; _D_, Dorsal fin; _C_, Heterocercal tail; _c_, notochord;
_n_, neurals; _h_, hæmals; 6–24, bucklers.]
SECOND SUB-ORDER--ACANTHODINI.
Extinct. _Body oblong, compressed, covered with shagreen; skull
not ossified; caudal heterocercal. Large spines, similar to those of
Chondropterygians, in front of some of the median and paired fins.
The spines are imbedded between the muscles, and not provided with a
proximal joint._
_Acanthodes_, _Chiracanthus_, from Devonian and Carboniferous
formations.
THIRD SUB-ORDER--DIPNOI.
_Nostrils two pairs, more or less within the mouth; limbs with
an axial skeleton. Lungs and gills. Skeleton notochordal. No
branchiostegals._[38]
FIRST FAMILY--SIRENIDÆ.
_Caudal fin diphycercal; no gular plates; scales cycloid. A pair of
molars, above and below, and one pair of vomerine teeth._
LEPIDOSIREN.--Body eel-shaped, with one continuous vertical fin.
Limbs reduced to cylindrical filaments, without fringe. Vomerine
teeth conical, pointed. Each dental lamina or molar with strong
cusps, supported by vertical ridges. No external branchial
appendages; five branchial arches, with four intervening clefts.
Conus arteriosus with two longitudinal valves. Ovaries closed
sacs.
One species only is known from the system of the River Amazons (_L.
paradoxa_). It must be very locally distributed, as but a few
specimens have been brought to Europe, and all recent endeavours to
obtain others have been unsuccessful. Natterer, by whom this most
interesting fish was discovered, states that he obtained two specimens,
one on the Madeira River, near Borba; the other in a backwater of the
Amazons, above Villa Nova. The natives of the former place called it
Carámurú, and considered it very scarce. The larger individual was
nearly four feet long. It is said to produce a sound not unlike that
of a cat, and to feed on the roots of mandioca and other vegetables.
But, to judge from the dentition, this fish is much more likely to be
carnivorous, like the following. It is one of the greatest desiderata
of Natural History Collections.
[Natterer, “Annalen des Wiener Museum’s,” 1839, ii.; Bischoff.
“Annales des Sciences Naturelles,” 1840. xiv.]
PROTOPTERUS.--Very similar in the general form of the body and
dentition to _Lepidosiren_. Pectoral and ventral filaments with
a fringe containing rays. Three small branchial appendages
above the small gill-opening; six branchial arches, with five
intervening clefts. Conus arteriosus with two longitudinal
valves. Ovaries closed sacs.
_Protopterus annectens_ is the “Lepidosiren” which is commonly found in
Zoological collections. It is usually imported from the west coast of
Africa, where it abounds in many localities; but it is spread over the
whole of tropical Africa, and forms in many districts of the central
parts a regular article of food.
[Illustration: Fig. 138.--Protopterus annectens. _g_,
Branchial filaments; _v_, vent.]
During the dry season, specimens living in shallow waters which
periodically dry up, form a cavity in the mud, the inside of which they
line with a protecting capsule of mucus, and from which they emerge
again when the rains refill the pools inhabited by them. Whilst they
remain in this torpid state of existence, the clay-balls containing
them are frequently dug out, and if the capsules are not broken, the
fishes imbedded in them can be transported to Europe, and released
by being immersed in slightly tepid water. _Protopterus_ is
exclusively carnivorous, feeding on water-insects, frogs, and fishes,
and attains a length of six feet.
[Owen, “Trans. Linn. Soc.” 1841, xviii.]
CERATODUS.--Body elongate, compressed, with one continuous
vertical fin. Limbs paddle-shaped, with broad, rayed fringe.
Vomerine teeth incisor-like; molars with flat, undulated
surface, and lateral prongs. No external branchial appendages.
Conus arteriosus with transverse series of valves. Ovaries
transversely lamellated.[39]
[Illustration: Fig. 139.--_Ceratodus miolepis._]
Two species, _C. forsteri_ and _C. miolepis_, are known from fresh
waters of Queensland. The specimens hitherto obtained have come from
the Burnett, Dawson, and Mary rivers, some from the fresh waters of
the upper parts, others from the lower brackish portions. The fish is
said to attain to a weight of twenty pounds and to a length of 6 feet.
Locally, the settlers call it “Flat-head,” “Burnett- or Dawson-Salmon,”
and the aborigines “Barramunda,” a name which they appear to apply
also to other large-scaled freshwater fishes, as the Osteoglossum
leichardti. In the stomach there is generally found an enormous
quantity of the leaves of plants growing on the banks of rivers,
evidently eaten after they had fallen into the water and when in a
decomposing condition. The flesh of the fish is salmon-coloured, and
much esteemed as food.
The Barramunda is said to be in the habit of going on land, or at least
on mud-flats; and this assertion appears to be borne out by the fact
that it is provided with a lung. However, it is much more probable
that it rises now and then to the surface of the water in order to
fill its lung with air, and then descends again until the air is so
much deoxygenised as to render a renewal of it necessary. It is also
said to make a grunting noise, which may be heard at night for some
distance. This noise is probably produced by the passage of the air
through the œsophagus when it is expelled for the purpose of renewal.
As the Barramunda has perfectly developed gills, beside the lung, we
can hardly doubt that, when it is in water of normal composition,
and sufficiently pure to yield the necessary supply of oxygen, these
organs are sufficient for the purpose of breathing, and that the
respiratory function rests with them alone. But when the fish is
compelled to sojourn in thick muddy water charged with gases, which are
the products of decomposing organic matter (and this must be the case
very frequently during the droughts which annually exhaust the creeks
of tropical Australia), it commences to breathe air with its lung in
the way indicated above. If the medium in which it happens to be is
perfectly unfit for breathing the gills cease to have any function;
if only in a less degree the gills may still continue to assist in
respiration. The Barramunda, in fact, can breathe by either gills or
lungs alone, or by both simultaneously. It is not probable that it
lives freely out of the water, its limbs being much too flexible for
supporting the heavy and unwieldy body, and too feeble generally to be
of much use in locomotion on land. However, it is quite possible that
it is occasionally compelled to leave the water, although we cannot
believe that it can exist without it in a lively condition for any
length of time.
Of its propagation or development we know nothing, except that it
deposits a great number of eggs of the size of those of a newt, and
enveloped in a gelatinous case. We may infer that the young are
provided with external gills, as in Protopterus and Polypterus.
[Illustration: Fig. 140.--Tooth of fossil _Ceratodus_ from
Aust., near Bristol, natural size.]
The discovery of _Ceratodus_ does not date farther back than the year
1870, and proved to be of the greatest interest, not only on account
of the relation of this creature to the other living _Dipnoi_ and
_Ganoidei_, but also because it threw fresh light on those singular
fossil teeth which are found in strata of Triassic and Jurassic
formations in various parts of Europe, India, and America. These teeth,
of which there is a great variety with regard to general shape and
size, are sometimes two inches long, much longer than broad, depressed,
with a flat or slightly undulated, always punctated crown, with one
margin convex, and with from three to seven prongs projecting on the
opposite margin.
[Illustration: Fig. 141.--Dipterus macrolepidotus.]
SECOND FAMILY--CTENODODIPTERIDÆ.
_Caudal fin heterocercal. Gular plates. Scales cycloid. Two pairs of
molars and one pair of vomerine teeth._
Extinct. _Dipterus_ (_Ctenodus_), _Heliodus_ from Devonian strata.
THIRD FAMILY--PHANEROPLEURIDÆ.
_Caudal fin diphycercal; vertical fin continuous. Gular plates.
Scales cycloid. Jaws with a series of minute conical teeth on the
margin._
Extinct. _Phaneropleuron_ from Devonian formations, and the
carboniferous _Uronemus_ are probably generically identical.
FOURTH SUB-ORDER--CHONDROSTEI.
_Skeleton notochordal; skull cartilaginous, with dermal ossifications;
branchiostegals few in number or absent. Teeth minute or absent.
Integuments naked or with bucklers. Caudal fin heterocercal, with
fulcra. Nostrils double, in front of the eyes._
FIRST FAMILY--ACIPENSERIDÆ.
_Body elongate, sub-cylindrical, with five rows of osseous bucklers.
Snout produced, subspatulate or conical, with the mouth at its lower
surface, small, transverse, protractile, toothless. Four barbels in a
transverse series on the lower side of the snout. Vertical fins with
a single series of fulcra in front. Dorsal and anal fins approximate
to the caudal. Gill-membranes confluent at the throat and attached to
the isthmus. Branchiostegals none. Gills four; two accessory gills.
Air-bladder large, simple, communicating with the dorsal wall of the
œsophagus._
[Illustration: Fig. 142.--Tail of Acipenser. _a_, Fulcra;
_b_, osseous bucklers.]
Sturgeons are, perhaps, the geologically youngest Ganoids, evidence
of their existence not having been met with hitherto in formations
of older date than the Eocene clay of Sheppey. They are exclusively
inhabitants of the temperate zone of the Northern Hemisphere, being
either entirely confined to fresh water, or passing, for the purpose of
spawning, a part of the year in rivers. They grow to a large size, and
are the largest fishes of the fresh waters of the Northern Hemisphere,
specimens 10 feet long being of common occurrence. The ova are very
small, and so numerous that one female has been calculated to produce
about three millions at one season; therefore their propagation, as
well as their growth, must be very rapid; and although in many rivers
their number is annually considerably thinned by the systematic manner
in which they are caught when they ascend the rivers in shoals from the
sea, no diminution has been observed. Wherever they occur they prove
to be most valuable on account of their wholesome flesh. In Russia,
besides, two not unimportant articles of trade are obtained from them,
viz. Caviare, which is prepared from their ovaries, and Isinglass,
which is made from the inner coats of their air-bladder. True Sturgeons
are divided into two genera, _Acipenser_ and _Scaphirhynchus_.
ACIPENSER.--The rows of osseous bucklers are not confluent
on the tail. Spiracles present. Caudal rays surrounding the
extremity of the tail.
About twenty different species of Sturgeons may be distinguished from
European, Asiatic, and American rivers. The best known are the Sterlet
(_A. ruthenus_) from Russian rivers, celebrated for the excellency of
its flesh, but rarely exceeding a length of three feet; the Californian
Short-snouted Sturgeon (_A. brachyrhynchus_); the Hausen (_A. huso_),
from rivers, falling into the Black Sea and the Sea of Azow (rare
in Mediterranean), sometimes 12 feet long, and yielding an inferior
kind of isinglass; the Chinese Sturgeon (_A. sinensis_); the Common
Sturgeon of the United States (_A. maculosus_), which sometimes crosses
the Atlantic to the coasts of Great Britain; Güldenstædt’s Sturgeon
(_A. güldenstædtii_), common in European and Asiatic rivers, which
yields more than one-fourth of the caviare and isinglass exported from
Russia; the Common Sturgeon of Western Europe (_A. sturio_), which
attains to a length of 18 feet, and has established itself also on the
coasts of Eastern North America.
SCAPHIRHYNCHUS.--Snout spatulate; posterior part of the tail
attenuated and depressed, so that it is entirely enveloped by
the osseous scutes. Spiracles none. The caudal rays do not
extend to the extremity of the tail, which terminates in a
filament.
Four species are known: one (_S. platyrhynchus_) from the
river-system of the Mississippi, and the three others from Central
Asia; all are exclusively freshwater fishes; their occurrence in so
widely distant rivers is one of the most striking instances by which
the close affinity of the North American and North Asiatic faunas is
proved.
SECOND FAMILY--POLYODONTIDÆ.
_Body naked, or with minute stellate ossifications. Mouth lateral,
very wide, with minute teeth in both jaws. Barbels none. Caudal fin
with fulcra. Dorsal and anal fins approximate to the caudal. Four gills
and a half; no opercular gill or pseudobranchia._
POLYODON (SPATULARIA).--The snout is produced into an
exceedingly long, shovel-like process, thin and flexible on
the sides. Spiracles present. Gill-cover terminating in a very
long tapering flap. One broad branchiostegal. Each branchial
arch with a double series of very long, fine, and numerous
gill-rakers, the two series being divided by a broad membrane.
Air-bladder cellular. Upper caudal fulcra narrow, numerous.
The single species, _P. folium_, occurs in the Mississippi, and grows
to a length of about six feet, of which the rostral shovel takes about
one-fourth; in young examples it is comparatively still longer.
PSEPHURUS differs from _Polyodon_ in having the rostral
process less depressed and more conical. The gill-rakers are
comparatively short, in moderate number, and distant from one
another. Upper caudal fulcra enormously developed, and in small
number (six).
_Psephurus gladius_ inhabits the Yan-tse-Kiang and Hoangho, the
distribution of the _Polyodontidæ_ being perfectly analogous to
that of _Scaphirhynchus_. It grows to an immense size, specimens
of 20 feet in length being mentioned by Basilewsky. The function of the
rostral process in the economy of these fishes is not yet sufficiently
explained. Martens believes that it serves as an organ of feeling,
the water of those large Asiatic and American rivers being too turbid
to admit of the Sturgeon seeing its prey, which consists of other
fishes. The eyes of _Psephurus_, as well as _Polyodon_, are
remarkably small. Both fishes are used as food.
[Illustration: Fig. 143.--Psephurus gladius.]
Allied to the _Polyodontidæ_, and likewise provided with a
paddle-shaped production of the fore part of the head, is the fossil
genus _Chondrosteus_, remains of which occur in the Lias.
FIFTH SUB-ORDER--POLYPTEROIDEI.
_Paired fins with axial skeleton, fringed; dorsal fins two or more.
Branchiostegals absent, but generally gular plates. Vertebral column
diphycercal or heterocercal. Body scaly._
FIRST FAMILY--POLYPTERIDÆ.
_Scales ganoid; fins without fulcra. A series of dorsal spines, to
each of which an articulated finlet is attached; anal placed close to
the caudal fin, the vent being near the end of the tail. Abdominal
portion of the vertebral column much longer than the caudal._
POLYPTERUS.--Teeth rasp-like, in broad bands in the jaws, on
the vomer and palatine bones; jaws with an outer series of
closely-set, larger, pointed teeth. Caudal fin surrounding the
extremity of the vertebral column; ventral fins well developed.
A spiracle on each side of the parietal, covered with an
osseous plate. A single large gular plate. Air-bladder double,
communicating with the ventral wall of the pharynx.
[Illustration: Fig. 144.--Polypterus bichir.]
This Ganoid is confined to tropical Africa, occurring in abundance in
the rivers of the west coast and in the Upper Nile; but it has not
been found in the river-systems belonging to the Indian Ocean. It is
scarce in the Middle and Lower Nile, and the specimens found below the
Cataracts have been carried down, from southern latitudes, and do not
propagate their species in that part of the river. There is only one
species known, _Polypterus bichir_ (“Bichir” being its vernacular
name in Egypt), which varies in the number of the dorsal finlets,
the lowest being eight, the highest eighteen. It attains to a length
of four feet. Nothing is known of its mode of life, and observations
thereon are very desirable.
CALAMOICHTHYS.--Distinguished from _Polypterus_ by its greatly
elongate form, and the absence of ventral fins.
_C. calabaricus_, a dwarf form from Old Calabar.
SECOND FAMILY--SAURODIPTERIDÆ.
_Scales ganoid, smooth like the surface of the skull. Two dorsal fins;
paired fins obtusely lobate. Teeth conical. Caudal heterocercal._
Extinct. _Diplopterus_, _Megalichthys_, and _Osteolepis_ from Devonian
and Carboniferous formations.
THIRD FAMILY--COELACANTHIDÆ.
_Scales cycloid. Two dorsal fins, each supported by a single
two-pronged interspinous bone; paired fins obtusely lobate. Air-bladder
ossified; notochord persistent, diphycercal._
Extinct. _Coelacanthus_ from carboniferous strata; several other
genera, from the coal formations to the chalk, have been associated
with it--_Undina_, _Graphiurus_, _Macropoma_, _Holophagus_,
_Hoplopygus_, _Rhizodus_.
FOURTH FAMILY--HOLOPTYCHIIDÆ.
_Scales cycloid or ganoid, sculptured. Two dorsal fins; pectorals
narrow, acutely lobate; dentition dendrodont._
Extinct. In this family a peculiar type of dentition is found--the
jaws are armed with two kinds of teeth, small ones serially arranged,
and much larger fang-like teeth disposed at long intervals. Both kinds
show at their base in transverse sections a labyrinthic complexity
of structure, numerous fissures radiating from the central mass of
vasodentine which fills up the pulp cavity, and sending off small
ramifying branches. Genera belonging to this family are _Holoptychius_,
_Saurichthys_, _Glyptolepis_, _Dendrodus_, _Glyptolaemus_,
_Glyptopomus_, _Tristichopterus_, _Gyroptychius_, _Strepsodus_, from
Devonian and Carboniferous strata.
SIXTH SUB-ORDER--PYCNODONTOIDEI.
_Body compressed, high and short or oval, covered with rhombic scales
arranged in decussating pleurolepidal lines. Notochord persistent.
Paired fins without axial skeleton. Teeth on the palate and hinder part
of the lower jaw molar-like. Branchiostegals, but no gular plates._
Extinct. The regular lozenge-shaped pattern of the integuments of these
fishes is described by Sir P. Egerton thus: “Each scale bears upon its
inner anterior margin a thick solid bony rib, extending upwards beyond
the margin of the scale, and sliced off obliquely, above and below, on
opposite sides, for forming splices with the corresponding processes
of the adjoining scales. These splices are so closely adjusted that,
without a magnifying power or an accidental dislocation, they are not
perceptible. When _in situ_, and seen internally, these continuous
lines decussate with the true vertebral apophyses.” In some genera the
“pleurolepidal” lines are confined to the anterior part of the side.
FIRST FAMILY--PLEUROLEPIDÆ.
_Homocercal. Body less high. Fins with fulcra._
_Pleurolepis_ and _Homoeolepis_ from the Lias.
SECOND FAMILY--PYCNODONTIDÆ.
_Homocercal. The neural arches and ribs are ossified; the roots of
the ribs are but little expanded in the older genera, but enlarged in
the tertiary forms, so as to simulate vertebræ. Paired fins not lobate.
Obtuse teeth on the palate and the sides of the mandible; maxilla
toothless; incisor-like teeth in the intermaxillary and front of the
mandible. Fulcra absent in all the fins._
These fishes abound in Mesozoic and Tertiary formations. _Gyrodus_,
_Mesturus_, _Microdon_, _Coelodus_, _Pycnodus_, _Mesodon_, are some of
the genera distinguished by palæontologists. (See Fig. 102, p. 201.)
SEVENTH SUB-ORDER--LEPIDOSTEOIDEI.
_Scales ganoid, rhombic; fins generally with fulcra; paired fins
not lobate. Præ- and inter-operculum developed; generally numerous
branchiostegals, but no gular plate._
FIRST FAMILY--LEPIDOSTEIDÆ.
_Scales ganoid, lozenge-shaped. Skeleton completely ossified;
vertebræ convex in front and concave behind. Fins with fulcra; dorsal
and anal composed of articulated rays only, placed far backwards, close
to the caudal. Abdominal part of the vertebral column much longer
than caudal. Branchiostegals not numerous, without enamelled surface.
Heterocercal._
_Lepidosteus._--Body elongate, sub-cylindrical; snout elongate,
spatulate, or beak-shaped; cleft of the mouth wide; both jaws
and palate armed with bands of rasp-like teeth and series
of larger conical teeth. Four gills; no spiracles; three
branchiostegals. Air-bladder cellular, communicating with the
pharynx.
[Illustration: Fig. 145.--Lepidosteus viridis.]
Fishes of this genus existed already in Tertiary times; their remains
have been found in Europe as well as North America. In our period
they are limited to the temperate parts of North America, Central
America, and Cuba. Three species can be distinguished which attain
to a length of about six feet. They feed on other fishes, and their
general resemblance to a pike has given to them the vernacular names of
“Gar-Pike,” or “Bony Pike.”
SECOND FAMILY--SAURIDÆ.
_Body oblong, with ganoid scales; vertebræ not completely ossified;
termination of the vertebral column homocercal; fins generally with
fulcra. Maxillary composed of a single piece; jaws with a single series
of conical pointed teeth. Branchiostegals numerous, enamelled, the
anterior broad gular plates._
Extinct. Numerous genera occur in Mesozoic formations; one with the
widest range is _Semionotus_, with distichous fulcra, from the Lias and
Jura; _Eugnathus_, with large posteriorly serrated scales, and fulcra
on nearly all fins; _Cephenoplosus_ from the Upper Lias; _Macrosemius_
from the Oolite; _Propterus_, _Ophiopsis_, _Pholidophorus_,
_Pleuropholis_, _Pachycormus_, _Oxygnathus_, _Ptycholepis_, _Conodus_,
_Eulepidotus_, _Lophiostomus_, etc.
THIRD FAMILY--STYLODONTIDÆ.
_Body rhombic or ovate, with ganoid scales; vertebræ not completely
ossified; termination of the vertebral column homocercal; fins with
fulcra. Maxillary composed of a single piece; jaws with several series
of teeth, the outer ones equal, styliform. Dorsal fin very long,
extending to the caudal. Branchiostegals numerous._
Extinct. _Tetragonolepis_ from the Lias (see Fig. 103, p. 207).
FOURTH FAMILY--SPHÆRODONTIDÆ.
_Body oblong, with rhombic ganoid scales; vertebræ ossified, but not
completely closed; homocercal; fins with fulcra. Maxillary composed of
a single piece; teeth in several series, obtuse; those on the palate
globular. Dorsal and anal fins short. Branchiostegals._
Extinct. The type genus of this family is _Lepidotus_, so named from
its large rhombic, dense, and polished scales. The dorsal is opposite
to the anal, and all the fins are provided with a double row of fulcra.
This genus ranges from the Lias to the Chalk; one species would seem
to have survived into tertiary times, if it should not prove to be a
_Lepidosteus_.
FIFTH FAMILY--ASPIDORHYNCHIDÆ.
_Body elongate, with ganoid scales; jaws prolonged into a beak;
termination of the vertebral column homocercal. Fins with fulcra;
a series of enlarged scales along the side of the body. Dorsal fin
opposite to the anal._
[Illustration: Fig. 146.--Aspidorhynchus fisheri, from the
Purbeck beds; _m_, mandible; _a_, presymphyseal bone.]
Extinct; mesozoic. _Aspidorhynchus_ has the upper jaw longer than the
lower; very peculiar is the occurrence of a single, solid, conical
bone, situated in front of the symphysis of the lower jaw, to which it
is joined by a suture. _Belonostomus_ with both jaws of equal length.
SIXTH FAMILY--PALÆONISCIDÆ.
_Body fusiform, with rhombic ganoid scales. Notochord persistent,
with the vertebral arches ossified. Heterocercal. All the fins with
fulcra; dorsal short. Branchiostegals numerous, the foremost pair
forming broad gulars. Teeth small, conical, or cylindrical._
Extinct. Many genera are known; from the Old Red
Sandstone--_Chirolepis_ and _Acrolepis_; from Carboniferous
rocks--_Cosmoptychius_, _Elonichthys_, _Nematoptychius_,
_Cycloptychius_, _Microconodus_, _Gonatodus_, _Rhadinichthys_,
_Myriolepis_, _Urosthenes_; from the Permian--_Rhabdolepis_,
_Palæoniscus_, _Amblypterus_ and _Pygopterus_; from the
Lias--_Centrolepis_, _Oxygnathus_, _Cosmolepis_, and _Thrissonotus_.
[See Traquair, “The Ganoid Fishes of the British Carboniferous
Formations.” Part I. _Palæoniscidæ._]
SEVENTH FAMILY--PLATYSOMIDÆ.
_Body generally high, compressed, covered with rhombic ganoid
scales arranged in dorso-ventral bands. Notochord persistent, with
the vertebral arches ossified. Heterocercal; fins with fulcra; dorsal
fin long, occupying the posterior half of the back. Branchiostegals
numerous. Teeth tubercular or obtuse._
Extinct. From Carboniferous and Permian formations--_Eurynotus_,
_Benedenius_, _Mesolepis_, _Eurysomus_, _Wardichthys_, _Chirodus_
(M’Coy), _Platysomus_.
[See Traquair, “On the Structure and Affinities of the Platysomidæ”, in
“Trans. Roy. Soc.,” Edinb., vol. xxix.]
[Illustration: Fig. 147.--Platysomus gibbosus.]
EIGHTH SUB-ORDER--AMIOIDEI.
_Vertebral column more or less completely ossified, heterocercal.
Body covered with cycloid scales. Branchiostegals present._
FIRST FAMILY--CATURIDÆ.
_Notochord persistent, with partially ossified vertebræ; homocercal;
fins with fulcra. Teeth in a single series, small, pointed._
Extinct. _Caturus_ from the Oolite to the Chalk.
[Illustration: Fig. 148.--Caturus furcatus (Solenhofen).]
SECOND FAMILY--LEPTOLEPIDÆ.
_Scales cycloid. Vertebræ ossified; homocercal; fins without fulcra;
dorsal short. Teeth minute, in bands, with canines in front._
Extinct, and leading to the living representative of this suborder.
_Thrissops_ with the dorsal fin placed far backwards, and opposite
to the long anal. _Leptolepis_ with the dorsal fin opposite to the
ventrals, from the Lias and Oolite. These fishes, as far as the
preserved parts are concerned, cannot be distinguished from Teleosteous
fishes, to which they are referred by some Palæontologists.
[Illustration: Fig. 149.--Leptolepis sprattiformis.]
THIRD FAMILY--AMIIDÆ.
_Skeleton entirely ossified; a single large gular plate; homocercal;
fins without fulcra; a long soft dorsal fin. Abdominal and caudal parts
of the vertebral column subequal in extent. Branchiostegals numerous._
[Illustration: Fig. 150.--Amia calva; _g_, gular plate.]
AMIA.--Body rather elongate, sub-cylindrical, compressed behind.
Snout short, cleft of the mouth of moderate width. Jaws with
an outer series of closely-set pointed teeth, and with a band
of rasp-like teeth; similar teeth on the vomer, palatine, and
pterygoid bones. Anal short; caudal fin rounded. Gills four;
air-bladder bifurcate in front, cellular, communicating with the
pharynx.
The “Bow-fin” or “Mud-fish” (_A. calva_) is not uncommon in many
of the fresh waters of the United States; it grows to a length of two
feet. Little is known about its habits; small fish, crustaceans, and
aquatic insects, have been found in its stomach. Wilder has observed
its respiratory actions; it rises to the surface, and, without emitting
any air-bubble whatever, opens the jaws widely, and apparently gulps in
a large quantity of air; these acts of respiration are more frequently
performed when the water is foul or has not been changed; and there
is no doubt that an exchange of oxygen and carbonic acid is effected,
as in the lungs of aërial vertebrates. The flesh of this fish is not
esteemed.
Fossil remains occur in tertiary deposits of North America, for
instance in the Wyoming territory; they have been distinguished as
_Protamia_ and _Hypamia_.
SECOND SUB-CLASS--TELEOSTEI.
_Heart with a non-contractile bulbus arteriosus; intestine without
spiral valve; optic nerves decussating; skeleton ossified, with
completely formed vertebræ; vertebral column diphycercal or homocercal;
branchiæ free._[40]
The Teleostei form the majority of the fishes of the present fauna, and
are the geological successors of the Palæichthyes, undoubted Teleostei
not ranging farther back than the Chalk. This sub-class comprises an
infinite variety of forms; and as, naturally, many Ganoid fishes lived
under similar external conditions, and led a similar mode of life as
certain Teleostei, we find not a few analogous forms in both series:
some Ganoids resembling externally the Teleosteous Siluroids, others
the Clupeoids, others the Chætodonts, others the Scombresoces, etc.
But there is no direct genetic relation between those fishes, as some
Naturalists were inclined to believe.
The Teleostei are divided into six orders:--
A. ACANTHOPTERYGII.--Part of the rays of the dorsal, anal, and
ventral fins not articulated, spines. The lower pharyngeals
separate. Air-bladder, if present, without pneumatic duct in the
adult.
B. ACANTHOPTERYGII PHARYNGOGNATHI.--Part of the rays of the
dorsal, anal, and ventral fins not articulated, spines. The
lower pharyngeals coalesced. Air-bladder without pneumatic duct.
C. ANACANTHINI.--Vertical and ventral fins without spinous rays.
Ventral fins, if present, jugular or thoracic. Air-bladder, if
present, without pneumatic duct. Lower pharyngeals separate.
D. PHYSOSTOMI.--All the fin rays articulated; only the first
of the dorsal and pectoral fins is sometimes ossified. Ventral
fins, if present, abdominal, without spine. Air-bladder, if
present, with a pneumatic duct.
E. LOPHOBRANCHII.--Gills not laminated, but composed of small
rounded lobes, attached to the branchial arches. Gill-cover
reduced to a large simple plate. A dermal skeleton replaces more
or less soft integuments.
F. PLECTOGNATHI.--A soft dorsal fin opposite to the anal;
sometimes elements of a spinous dorsal. Ventral fins none,
or reduced to spines. Gills pectinate; air-bladder without
pneumatic duct. Skin with rough scutes, or with spines, or naked.
FIRST ORDER--ACANTHOPTERYGII.
_Part of the rays of the dorsal, anal, and ventral fins are not
articulated, more or less pungent spines. The lower pharyngeals are
generally separate. Air-bladder, if present, without pneumatic duct in
the adult._[41]
FIRST DIVISION--ACANTHOPTERYGII PERCIFORMES.
_Body more or less compressed, elevated or oblong, but not elongate;
the vent is remote from the extremity of the tail, behind the ventral
fins if they are present. No prominent anal papilla. No superbranchial
organ. Dorsal fin or fins occupying the greater portion of the
back; spinous dorsal well developed, generally with stiff spines, of
moderate extent, rather longer than, or as long as, the soft; the soft
anal similar to the soft dorsal, of moderate extent or rather short.
Ventrals thoracic, with one spine and with four or five rays._
FIRST FAMILY--PERCIDÆ.
_The scales extend but rarely over the vertical fins, and the lateral
line is generally present, continuous from the head to the caudal fin.
All the teeth simple and conical; no barbels. No bony stay for the
præoperculum._
A large family, represented by numerous genera and species in fresh
waters, and on all the coasts of the temperate and tropical regions.
Carnivorous.
Fossil Percoids abound in some formations, for instance, at Monte
Bolca, where species of _Labrax_, _Lates_, _Smerdis_ and _Cyclopoma_
(both extinct), _Dules_, _Serranus_, _Apogon_, _Therapon_, and
_Pristipoma_ have been recognised. _Paraperca_ is a genus recently
discovered in the Marles of Aix-en-Provence. A species of _Perca_ is
known from the freshwater deposit of Oeningen.
PERCA.--All the teeth are villiform, without canines; teeth
on the palatine bones and vomer; tongue toothless. Two dorsal
fins, the first with thirteen or fourteen spines; anal fin with
two spines. Præoperculum and præorbital serrated. Scales small;
head naked above. Branchiostegals seven. Vertebræ more than
twenty-four.
The “Freshwater Perch” (_Perca fluviatilis_) is too familiarly known
to require description. It is generally distributed over Europe and
Northern Asia; and equally common in North America, there being no
sufficient ground for separating specifically the specimens of the
Western Hemisphere. It frequents especially still waters, and sometimes
descends into brackish water. Its weight does not seem to exceed 5
lbs. The female deposits her ova, united together by a viscid matter,
in lengthened or net-shaped bands, on waterplants. The number of
the eggs of one spawn may exceed a million. Two other species, _P.
gracilis_, from Canada, and _P. schrenckii_, from Turkestan, have been
distinguished, but they are very imperfectly known. An allied genus is
_Siniperca_, from Northern China.
[Illustration: Fig. 151.--Perca fluviatilis, the Perch.]
PERCICHTHYS.--Differing from _Perca_ especially in the number of
the fin-spines, which are nine or ten in the first dorsal, and
three in the anal fin. The upper surface of the head scaly.
These fishes represent the Freshwater Perches of the Northern
Hemisphere in the fresh waters of the temperate parts of South America.
Two species have been described from Patagonia, and one or two from
Chili and Peru.
LABRAX.--All the teeth are villiform, without canines;
teeth on the palatine bones, vomer, and the tongue. Two dorsal
fins, the first with nine spines; anal fin generally with three.
Præoperculum serrated, and with denticulations along its lower
limb; præorbital with the margin entire. Scales rather small.
Branchiostegals seven; well developed pseudobranchiæ.
The “Bass” are fishes common on the coasts of Europe and the Atlantic
coasts, and in the fresh waters of the United States and Canada. The
three European species are almost exclusively inhabitants of the sea,
entering brackish, but never fresh waters, whilst the American species,
the number of which is still uncertain, seem to affect principally
fresh water, although some are also found in the sea. The best known
European species is _Labrax lupus_ (see p. 41, Fig. 4), common on
the British coasts. It is a voracious fish, with a remarkably large
stomach, and received from the ancient Romans the appropriate name of
_lupus_. By the Greeks it was so highly esteemed that Archestratus
termed this or one of the two other closely-allied species, taken near
Milet, “offspring of the gods.” They attributed to it a tender regard
for its own safety; and Aristotle says that it is the most cunning of
fishes; and that, when surrounded by the net, it digs for itself a
channel of escape through the sand. Specimens of from two to three feet
are not scarce, but its flesh is nowadays much less esteemed than in
ancient times. Of the North American species _Labrax lineatus_ and
_Labrax rufus_ are the most common.
LATES.--All the teeth are villiform, without canines; teeth on
the palatine bones and vomer, but none on the tongue. Two dorsal
fins--the first with seven or eight, the anal fin with two or
three, spines. Præoperculum with strong spines at the angle and
the lower limb; also the præorbital is strongly serrated. Scales
of moderate size. Branchiostegals seven; pseudobranchiæ present.
Three well-known species belong to this genus. The Perch of the Nile
and other rivers of tropical Africa (_Lates niloticus_); the Perch of
the Ganges and other East Indian rivers, which enters freely brackish
water, and extends to the rivers of Queensland (_Lates calcarifer_).
These two species attain to a large size, the Indian species to a
length of five feet. Hamilton says that “the vulgar English in Calcutta
call it ‘Cockup,’ and that it is one of the lightest and most esteemed
foods brought to table in that city.” Specimens two feet in length and
caught in salt water are by far the best quality. The third species
(_Lates colonorum_) is found in Australia only, and does not appear to
grow to the same large size as its congeners.
Allied to _Lates_ is _Psammoperca_ from Australia.
PERCALABRAX.--All the teeth villiform, without canines; teeth on
the palatine bones and vomer, but none on the tongue. Two dorsal
fins--the first with eleven, the anal fin with three spines.
Præoperculum serrated along its hinder margin, and with strong
spinous teeth below; præorbital not serrated. Scales rather
small. Branchiostegals seven; pseudobranchiæ present.
This Perch (_Percalabrax japonicus_) is one of the most common fishes
on the coasts of China, Japan, and Formosa; the Japanese name it
“Zuzuki,” or “Seengo.”
ACERINA.--All the teeth villiform, without canines; teeth on
the vomer, but none on the palatine bones or the tongue. One
continuous dorsal fin, of which the spinous portion consists of
from thirteen to nineteen spines; two anal spines. Body rather
low, with rather small scales. Bones of the skull with wide
muciferous cavities; præoperculum denticulated.
Small freshwater perches, of which _A. cernua_, named “Pope” in
England, is the most common, and has the widest distribution in Central
Europe and Siberia. The two other species have a more restricted range,
_A. schrætzer_ being confined to the Danube and other rivers
emptying into the Black Sea; and _A. czekanowskii_ to Siberian
rivers. This genus is not represented in the Western Hemisphere.
LUCIOPERCA.--Teeth in villiform bands, those in the jaws with
additional canines; palatine bones toothed. Two dorsal fins--the
first with from twelve to fourteen, the anal fin with two
spines. Præoperculum serrated; scales small.
The “Pike-Perches” are inhabitants of many lakes and rivers of the
temperate northern zone. The European species is confined to the
eastern two-thirds of the continent, and one of the most esteemed
freshwater fishes; it attains to a length of three or four feet,
and to a weight of from 25 to 30 lbs. It has been recommended for
acclimatisation in England, and there is no doubt that in certain
localities it might prove a valuable addition to the native fauna; but
like all its congeners it is very voracious and destructive to smaller
fishes. Two other species inhabit rivers of European and Asiatic
Russia, and two or three the fresh waters of North America.
PILEOMA.--All the teeth minute, villiform, without canines;
teeth on the vomer and palatine bones. Two dorsal fins--the
first with fourteen or fifteen spines. Body rather elongate,
with small scales. Præoperculum not serrated.
Small freshwater perches abundant in the United States. Like the
following genus, and some others which need not be mentioned here,
they can be regarded as small, dwarfed representatives of the
preceding genera. The species seem to be numerous, but have not yet
been sufficiently well distinguished. The latest and best account of
them is by L. Vaillant, “Recherches sur les Poissons d’eaux douces de
l’Amérique septentrionale (_Etheostomatidæ_),” in Nouv. Archiv. du
Muséum d’Hist. Nat. de Paris, ix., 1873.
BOLEOSOMA.--Allied to _Pileoma_, but with only nine or ten
feeble spines in the first dorsal fin. North America.
ASPRO.--Body elongate, cylindrical; snout thick, projecting
beyond the mouth, which is situated at its lower side. All
the teeth villiform, without canines; teeth on the vomer and
palatine bones. Two separate dorsals. Præoperculum serrated;
præorbital entire. Scales small.
Two small Perches from the Danube and some other rivers of the
continent of Europe, _Aspro vulgaris_ and _A. zingel_.
CENTROPOMUS.--Body oblong, compressed, with scales of
moderate size. All the teeth villiform, without canines; teeth
on the vomer and palatine bones. Two dorsal fins, the first with
eight strong spines, the anal with three, the second of which is
very strong and long. Præoperculum with a double denticulated
edge.
Numerous species are known from the West Indies and Central America.
These fishes are found in fresh, brackish, and salt water, and some of
the species indiscriminately enter all three kinds of water. They do
not grow to any large size, but are esteemed as food.
ENOPLOSUS.--Body much elevated, the depth being still more
increased by the high vertical fins. All the teeth are
villiform, without canines; teeth on the vomer, palatine bones,
and the tongue. Two dorsal fins, the first with seven spines.
Præoperculum serrated, with spinous teeth at the angle. Scales
of moderate size.
A small and very common marine species (_E. armatus_) on the coast
of Australia, especially New South Wales. It is readily recognised by
the peculiar shape of its body, and eight black transverse bands on a
whitish ground.
* * * * *
This, and the preceding genus, leads to the true “Sea perches,” which
never, or but rarely, enter fresh water:--
CENTROPRISTIS.--Body oblong, with scales of small or moderate
size. Teeth villiform, with small canines in both jaws; vomerine
teeth placed in an angular band, or a short triangular patch;
teeth on the palatine bones, but none on the tongue. One dorsal,
with the formula 10/12 or less; anal fin 3/7(6). Præoperculum
serrated; sometimes with the angle projecting, and armed with
long spines.
About twenty species of small size are known from temperate and
tropical seas.
ANTHIAS.--Body rather short, compressed, with scales of moderate
size. Teeth villiform, with small canines in both jaws; teeth on the
vomer, and palatine teeth. One dorsal, generally with ten spines; anal
fin with three; caudal forked. The rays of one or more fins may be
prolonged. Præoperculum serrated.
About twenty species are known from temperate and tropical seas; they
are mostly of small size, and agreeably coloured, pink and yellow
being the predominant colours. _Anthias sacer_ is common in the
Mediterranean, and was well known to the ancients. Aristotle says that
the fishers of Sponges call it sacred, because no voracious fishes came
to the places which it frequented, and the diver might descend with
safety.--_Callanthias_ is a genus closely allied to _Anthias_.
SERRANUS.--Body oblong, compressed, with small scales. Teeth
villiform, with very distinct canines in both jaws; teeth on the
vomer and palatine bones, none on the tongue. One dorsal, mostly
with nine or eleven, rarely with eight, ten or twelve spines;
anal fin with three: all the spines being stout. Præoperculum
serrated behind and at the angle, but not below.
[Illustration: Fig. 152.--Serranus altivelis.]
The “Sea perches proper” are found on the shores of all temperate and
tropical seas, most abundantly in the latter. A few species enter
brackish and even fresh water, one having been found as high up the
Ganges as the confines of Nepal. However, all spawn in the sea. The
variety of species is almost infinite, about 150 being tolerably
well known, and many more having been described. The distinction of
the species is most difficult, and nearly impossible to those who
have no opportunity of closely and long observing them in nature,
as they are not only subject to great variation of colour, but also
to considerable changes dependent on age. Many are most agreeably
coloured, and ornamented with spots, or cross bands or longitudinal
stripes; colours which become more uniform with age in those species
which attain to a large size. The majority remain of rather small
size, growing to a length of one or two feet; but not a few reach
more than twice that length, and may even become dangerous to man.
Instances of bathers having been attacked by a gigantic species not
uncommon at the Seychelles and Aden are on record, the persons having
died from the injuries received. Almost all the species are eatable,
and many are esteemed as food. One species is common on the British
coasts (_S. cabrilla_), and probably some of the more southern species
(_S. scriba_ and _S. gigas_) occasionally wander as far northwards as
the British Channel. The species figured, _S. altvelis_, is locally
distributed over nearly all the tropical parts of the Indian Ocean, and
distinguished by particularly high dorsal and anal fins. _Anyperodon_
and _Prionodes_ are two genera closely allied to _Serranus_.
PLECTROPOMA.--Form of the body and dentition (see p. 127, Fig.
54) similar to that of _Serranus_, with a præoperculum serrated
behind, and armed with spinous teeth below, which are directed
forwards. Dorsal fin with from seven to thirteen spines.
About thirty species from tropical seas are known. _Trachypoma_ is
allied to this genus.
POLYPRION.--Body oblong, rather compressed, covered with small
scales. All the teeth are villiform; teeth on the vomer,
palatine bones, and the tongue. One dorsal with eleven or twelve
spines; anal with three. Præoperculum denticulated; a strong,
rough, longitudinal ridge on the operculum.
Two species are known: one from the European coasts (_P. cernium_),
and one from Juan Fernandez (_P. kneri_). They attain to a weight of
80 lbs. and more. The European species has the habit of accompanying
floating wood, to which they are attracted by the small marine species
generally surrounding such objects, and affording a supply of food. It
is known by the name of “Stone-bass,” and excellent eating.
GRAMMISTES.--Body rather short, compressed, covered with minute
scales imbedded in the thick skin. All the teeth are villiform;
teeth on the vomer and palatine bones. Two dorsal fins, the
first with seven spines. Præoperculum without serrature, but
with three short spines. A short skinny barbel is frequently
developed at the chin.
Three species are known from the Indo-Pacific; they are of small
size. One, _G. orientalis_, is black, with six or seven white
longitudinal stripes, and one of the most common coast-fishes of that
ocean.
RHYPTICUS.--Body oblong, compressed, covered with minute scales
imbedded in the thick skin. All the teeth are villiform; teeth
on the vomer and palatine bones. The spines of the vertical fins
are but little developed, always in small number and short, and
may disappear entirely. Præoperculum not serrated, with some
obtuse spines.
Four species are known: three from the West Indies and one from the
Galapagoes Islands.
Other genera allied to the two preceding are _Aulacocephalus_ from
Mauritius, Reunion, and Japan; and _Myriodon_ from the coasts of
Australia.
DIPLOPRION.--Body rather elevated, compressed, with small
scales. All the teeth villiform; teeth on the vomer and palatine
bones. Two dorsal fins, the first with eight spines; anal with
two. Præoperculum with a double denticulated limb.
[Illustration: Fig. 153.--Mesoprion monostigma.]
The single species known (_D. bifasciatum_), is very common in the East
Indian Archipelago, and on the coasts of Southern China and Japan. It
is of small size, and ornamented with two broad black cross-bands.
MESOPRION.--Body oblong, compressed, covered with scales of
moderate size. Teeth villiform, with canines in both jaws;
teeth on the vomer and palatine bones. One dorsal fin, with
ten or eleven, rarely with more spines; anal fin with three.
Præoperculum serrated; in some species (_Genyoroge_) a more or
less distinct spinous knob projects from the surface of the
interoperculum, and is received in a more or less deep notch of
the præopercular margin.
[Illustration: Fig. 154.--Opercles _a_, of _Mesoprion_;
_b_, of _Genyoroge_; _o_, knob received in a notch
of the præoperculum.]
About seventy species are known from tropical seas in both hemispheres,
but it is noteworthy that the species with the peculiar protuberance
of the interoperculum are confined to the Indo-Pacific. The coloration
is much more simple than in the small-scaled Serrani, a uniform hue
of greenish, pink, or red prevailing; species with longitudinal bands
are scarce, but not rarely dark cross-bands or a large spot on the
side occur. The majority of the species remain within very moderate
dimensions, specimens exceeding three feet in length being scarce. They
are generally eaten, and some of the species belong to the commonest
fishes of the tropics, as _M. bengalensis_, _chrysurus_, _gembra_,
_griseus_, and others.
_Glaucosoma_ from Japan and Australia is allied to _Mesoprion_.
DULES.--Body oblong, compressed, with scales of moderate size,
and very indistinctly ctenoid. All the teeth are villiform;
teeth on the vomer and palatine bones. One dorsal with ten
spines; anal fin with three. Præoperculum serrated. Six
branchiostegals only.
About ten species are known, inhabiting fresh waters of the coasts of
the Indo-Pacific, and being especially common in the islands of this
region, and also in Tropical Australia. Some live also in brackish
water. Though of small size they are esteemed as food.
THERAPON.--Body oblong, compressed, with scales of moderate
size. All the teeth are villiform, those of the vomer and
palatine bones being rudimentary, and frequently absent. One
dorsal, with a depression in its upper margin, and twelve or
thirteen spines; anal fin with three. Præoperculum serrated.
Air-bladder with two divisions, an anterior and posterior. Six
branchiostegals.
About twenty species are known, the distribution of which nearly
coincides with _Dules_, but as some of the species are more or less
marine, the genus is spread over the whole area of the tropical
Indo-Pacific. Other species, especially those of Australian rivers,
are entirely limited to fresh water. _Th. theraps_, _Th. servus_, and
_Th. cuvieri_ belong to the most common fishes of that area, extending
from the east coast of Africa to Polynesia. They are readily recognised
by the blackish longitudinal bands with which the body is ornamented.
All the species are of small size. _Helotes_ is closely allied to this
genus.
PRISTIPOMA.--Body oblong, compressed, with ctenoid scales of
moderate size. Cleft of the mouth horizontal, not very wide,
with the jaws nearly equal in length anteriorly; a central pit
below the chin; villiform teeth in the jaws without canines;
palate toothless. One dorsal, with eleven to fourteen spines;
anal with three. Vertical fins not scaly, or with scales along
the base only. Præoperculum serrated. Branchiostegals, seven.
[Illustration: Fig. 155.--Lower view of mandible of Pristipoma
manadense.]
About forty species are known, all from the sea. They are extremely
common between the tropics, some of the species extending into the
neighbouring sub-tropical parts. They do not attain a large size, and
generally have a plain coloration. _Conodon_ is an allied genus.
[Illustration: Fig. 156.--Hæmulon brevirostrum.]
HÆMULON.--Body oblong, compressed, with ctenoid scales of
moderate size. Cleft of the mouth horizontal, generally wide,
with the jaws equal in length anteriorly; a central pit below
the chin; villiform teeth in the jaws, without canines; palate
toothless. One dorsal, with twelve or thirteen spines; anal with
three; the soft portions of the vertical fins scaly to their
margins. Præoperculum serrated. Branchiostegals, seven.
Marine; sixteen species are known from the coasts of Tropical America;
they are of rather small size. The species figured occurs on both sides
of Central America. _Hapalogenys_ is an allied genus.
DIAGRAMMA.--Body oblong, compressed, covered with rather small
ctenoid scales. Upper profile of the head parabolic; cleft of
the mouth small, horizontal; from four to six pores under the
mandible, but without central pit. Teeth villiform, without
canines; palate toothless. One dorsal fin, with from nine to
fourteen spines; anal with three. Vertical fins not scaly.
Præoperculum serrated; infraorbital not armed. Branchiostegals,
six or seven.
[Illustration: Fig. 157.--Diagramma orientale, from the
Indo-Pacific.]
Forty species are known, which, with very few exceptions, belong to
the tropical parts of the Indo-Pacific. Some attain to a size not very
common among Sea-Perches, viz. to a length of from three to four feet.
Many are agreeably coloured with black bands or spots. All appear to be
esteemed as food. _Hyperoglyphe_ from Australia is allied to this
genus.
LOBOTES.--Body rather elevated, compressed, with ctenoid scales
of moderate size. Eye rather small. Snout obtuse, with oblique
cleft of the mouth, and with the lower jaw longest. Teeth
villiform, without canines; palate toothless. One dorsal fin
with twelve spines; anal with three. Præoperculum denticulated.
Branchiostegals, six.
A remarkable fish (_L. auctorum_) on account of its extraordinary
range. Common in many localities, scarcer in others, it occurs in the
East Indies, and on all the Atlantic coasts of tropical and temperate
America. Döderlein found it on the coast of Sicily in 1875. It lives in
salt and brackish water, and is known to attain to a length of two feet.
HISTIOPTERUS.--Body rather elevated, strongly compressed, with
very small scales. Snout much produced, the anterior profile of
the head being concave. Mouth small, at the end of the snout.
Teeth villiform, without canines; palate toothless. Some of the
spines and rays of the vertical and pectoral fins very long. One
dorsal, with about ten spines; anal with three. Præopercular
margin partly serrated. Branchiostegals, six.
Marine. Four species are known from Japan and South Australia. The
species figured attains to a length of 20 inches, and is esteemed as
food. It is known at Melbourne by the names of “Boar Fish” or “Bastard
Dorey.”
[Illustration: Fig. 158.--Histiopterus recurvirostris.]
GERRES.--Body oblong, or rather elevated, covered with scales
of moderate size, which are either entirely smooth or minutely
ciliated. Mouth very protractile, and descending when thrust
out. Eye rather large. No canine teeth; dentition feeble, and
palate toothless. The two divisions of the dorsal fin are nearly
separated by a deep incision. Formula of the vertical fins--D.
9/10 A. 2·3/7·9. Caudal fin forked. Præoperculum generally
without denticulation. Lower pharyngeal bones coalescent.
[Illustration: Fig. 159.--Gerres altispinis, from the mouth of
the Ganges.]
More than thirty species are known of this genus, which bear so close a
resemblance to one another that their distinction is rather difficult.
They live in the seas between the Tropics, and some, perhaps all, of
the species enter fresh water. Very rarely they exceed a length of ten
inches; nearly all have a plain silvery coloration. The coalescence
of their lower pharyngeals renders their systematic position rather
uncertain, and, indeed, some Ichthyologists have referred them to the
Pharyngognaths.
SCOLOPSIS.--Body oblong, covered with scales finely serrated
and of moderate size. Jaws nearly equal in length anteriorly;
cleft of the mouth horizontal. Teeth villiform, without canines;
palate toothless. One dorsal fin. Formula of the vertical fins:
D. 10/9 A. 3/7. Caudal fin forked. Præoperculum distinctly
denticulated; infraorbital ring with a spine directed backwards.
Branchiostegals, five.
[Illustration: Fig. 160.--Infraorbital spine of Scolopsis
monogramma.]
Marine, and of small size. Twenty-five species are known from the
tropical parts of the Indo-Pacific. _Heterognathodon_ is an allied
genus, but without the infraorbital spine.