THE GANOIDS—Continued
=CLASSIFICATION of Ganoids.=—The subdivision of the series of Ganoidei
into orders offers great difficulty from the fact of the varying
relationships of the members of the group and the fact that the great
majority of the species are known only from broken skeletons preserved
in the rocks. It is apparently easy to separate those with cartilaginous
skeletons from those with these bones more or less ossified. It is also
easy to separate those with bony scales or plates from those having the
scales cycloid. But the one type of skeleton grades into the other, and
there is a bony basis even to the thinnest of scales found in this
group. Among the multitude of names and divisions proposed we may
recognize six orders, for which the names _Lysopteri_, _Chondrostei_,
_Selachostomi_, _Pycnodonti_, _Lepidostei_, and _Halecomorphi_ are not
inappropriate. Each of these seems to represent a distinct offshoot from
the first primitive group.
=Order Lysopteri.=—In the most primitive order, called _Lysopteri_
(λυσός, loose; πτερόν, fin) by Cope, _Heterocerci_ by Zittel and
Eastman, and the "ascending series of Chondrostei" by Woodward, we find
the nearest approach to the Chondropterygians. In this order the arches
of the vertebræ are more or less ossified, the body is more or less
short and deep, covered with bony dermal plates. The opercular apparatus
is well developed, with numerous branchiostegals. Infraclavicles are
present, and the fins provided with fulcra. Dorsal and anal fins are
present, with rays more numerous than their supports; ventral fin with
basal supports which are imperfectly ossified; caudal fin mostly
heterocercal, the scales mostly rhombic in form. All the members of this
group are now extinct.
=The Palæoniscidæ.=—The numerous genera of this order are referred to
three families, the _Palæoniscidæ_, _Platysomidæ_, and _Dictyopygidæ_; a
fourth family, _Dorypteridæ_, of uncertain relations, being also
tentatively recognized. The family of _Palæoniscidæ_ is the most
primitive, ranging from the Devonian to the Lias, and some of them seem
to have entered fresh waters in the time of the coal-measures. These
fishes have the body elongate and provided with one short dorsal fin.
The tail is heterocercal and the body covered with rhombic plates.
Fulcra or rudimentary spine-like scales are developed on the upper edge
of the caudal fin in most recent Ganoids, and often the back has a
median row of undeveloped scales. A multitude of species and genera are
recorded. A typical form is the genus _Palæoniscum_,[5] with many
species represented in the rocks of various parts of the world. The
longest known species is _Palæoniscum frieslebenense_ from the Permian
of Germany and England. _Palæoniscum magnum_, sixteen inches long,
occurs in the Permian of Germany. From _Canobius_, the most primitive
genus, to _Coccolepis_, the most modern, is a continuous series, the
suspensorium of the lower jaw becoming more oblique, the basal bones of
the dorsal fewer, the dorsal extending farther forward, and the scales
more completely imbricate. Other prominent genera are _Amblypterus_,
_Eurylepis_, _Cheirolepis_, _Rhadinichthys_, _Pygopterus_,
_Elonichthys_, _Ærolepis_, _Gyrolepis_, _Myriolepis_, _Oxygnathus_,
_Centrolepis_, and _Holurus_.
Footnote 5:
This word is usually written _Palæoniscus_, but Blainville, its author
(1818), chose the neuter form.
[Illustration:
FIG. 2.—_Palæoniscum frieslebenense_ Blainville. Family
_Palæoniscidæ_. (After Zittel.)
]
=The Platysomidæ.=—The _Platysomidæ_ are different in form, the body
being deep and compressed, often diamond-shaped, with very long dorsal
and anal fins. In other respects they are very similar to the
_Palæoniscidæ_, the osteology being the same. The _Palæoniscidæ_ were
rapacious fishes with sharp teeth, the _Platysomidæ_ less active, and,
from the blunter teeth, probably feeding on small animals, as crabs and
snails.
The rhombic enameled scales are highly specialized and held together as
a coat of mail by peg-and-socket joints. The most extreme form is
_Platysomus_, with the body very deep. _Platysomus gibbosus_ and other
species occur in the Permian rocks of Germany. _Cheirodus_ is similar to
_Platysomus_, but without ventral fins. _Eurynotus_, the most primitive
genus, is remarkable for its large pectoral fins. _Eurynotus crenatus_
occurs in the Subcarboniferous of Scotland. Other genera are
_Mesolepis_, _Globulodus_, _Wardichthys_, and _Cheirodopsis_.
[Illustration:
FIG. 3.—_Eurynotus crenatus_ Agassiz, restored. Carboniferous. Family
_Platysomidæ_. (After Traquair.)
]
Some of the _Platysomidæ_ have the interneural spines projecting through
the skin before the dorsal fin. This condition is found also in certain
bony fishes allied to the _Carangidæ_.
=The Dorypteridæ.=—_Dorypterus hoffmani_, the type of the singular
Palæozoic family of _Dorypteridæ_, with thoracic or sub-jugular
many-rayed ventrals, is Stromateus-like to all appearance, with distinct
resemblances to certain Scombroid forms, but with a heterocercal tail
like a ganoid, imperfectly ossified back-bone, and other very archaic
characters. The body is apparently scaleless, unlike the true
_Platysomidæ_, in which the scales are highly developed. A second
species, _Dorypterus althausi_, also from the German copper shales, has
been described. This species has lower fins than _Dorypterus hoffmani_,
but may be the adult of the same type. _Dorypterus_ is regarded by
Woodward as a specialized offshoot from the _Platysomidæ_. The
many-rayed ventrals and the general form of the body and fins suggest
affinity with the _Lampridæ_.
[Illustration:
FIG. 4.—_Dorypterus hoffmani_ Germar, restored. (After Hancock and
Howse.)
]
=Dictyopygidæ.=—In the _Dictyopygidæ_ (_Catopteridæ_), the body is
gracefully elongate, less compressed, the heterocercal tail is short and
abruptly turned upwards, the teeth are sharp and usually hooked, and the
bony plates well developed. Of this group two genera are recognized,
each containing numerous species. In _Redfieldius_ (= _Catopterus_
Redfield, not of Agassiz) the dorsal is inserted behind the anal, while
in _Dictyopyge_ this is not the case. _Redfieldius gracilis_ and other
species are found in the Triassic of the Connecticut River. _Dictyopyge
macrura_ is found in the same region, and _Dictyopyge catoptera_ and
other species in Europe.
=Order Chondrostei.=—The order _Chondrostei_ (χόνδρος, cartilage;
ὀστέον, bone), as accepted by Woodward, is characterized by the
persistence of the notochord in greater or less degree, the endoskeleton
remaining cartilaginous. In all, the axonosts and baseosts of the median
fins are arranged in simple regular series and the rays are more
numerous than the supporting elements. The shoulder-girdle has a pair of
infraclavicular plates. The pelvic fins have well-developed baseosts.
The branchiostegals are few or wanting. In the living forms, and
probably in all others, a matter which can never be ascertained, the
optic nerves are not decussating, but form an optic chiasma, and the
intestine is provided with a spiral valve. In all the species there is
one dorsal and one anal fin, separate from the caudal. The teeth are
small or wanting, the body naked or covered with bony plates; the caudal
fin is usually heterocercal, and on the tail are rhombic plates. To this
order, as thus defined, about half of the extinct Ganoids belong, as
well as the modern degenerate forms known as sturgeons and perhaps the
paddle-fishes, which are apparently derived from fishes with rhombic
enameled scales. The species extend from the Upper Carboniferous to the
present time, being most numerous in the Triassic.
At this point in Woodward's system diverges a descending series,
characterized as a whole by imperfect squamation and elongate form, this
leading through the synthetic type of _Chondrosteidæ_ to the modern
sturgeon and paddle-fish, which are regarded as degenerate types.
The family of _Saurorhynchidæ_ contains pike-like forms, with long jaws,
and long conical teeth set wide apart. The tail is not heterocercal, but
short-diphycercal; the bones of the head are covered with enamel, and
those of the roof of the skull form a continuous shield. The opercular
apparatus is much reduced, and there are no branchiostegals. The fins
are all small, without fulcra, and the skin has isolated longitudinal
series of bony scutes, but is not covered with continuous scales. The
principal genus is _Saurorhynchus_ (= _Belonorhynchus_; the former being
the earlier name) from the Triassic. _Saurorhynchus acutus_ from the
English Triassic is the best known species.
The family of _Chondrosteidæ_ includes the Triassic precursors of the
sturgeons. The general form is that of the sturgeon, but the body is
scaleless except on the upper caudal lobe, and there are no plates on
the median line of the skull. The opercle and subopercle are present,
the jaws are toothless, and there are a few well-developed caudal rays.
The caudal has large fulcra. The single well-known species of this
group, _Chondrosteus acipenseroides_, is found in the Triassic rocks of
England and reaches a length of about three feet. It much resembles a
modern sturgeon, though differing in several technical respects.
_Chondrosteus pachyurus_ is based on the tail of a species of much
larger size and _Gyrosteus mirabilis_, also of the English Triassic, is
known from fragments of fishes which must have been 18 to 20 feet in
length.
[Illustration:
FIG. 5.—_Chondrosteus acipenseroides_ Egerton. Family _Chondrosteidæ_.
(After Woodward.)
]
The sturgeons constitute the recent family of _Acipenseridæ_,
characterized by the prolonged snout and toothless jaws and the presence
of four barbels below the snout. In the _Acipenseridæ_ there are no
branchiostegals and a median series of plates is present on the head.
The body is armed with five rows of large bony bucklers,—each often with
a hooked spine, sharpest in the young. Besides these, rhombic plates are
developed on the tail, besides large fulcra. The sturgeons are the
youngest of the Ganoids, not occurring before the Lower Eocene, one
species, _Acipenser toliapicus_ occurring in the London clay. About
thirty living species of sturgeon are known, referred to three genera:
_Acipenser_, found throughout the Northern Hemisphere, _Scaphirhynchus_,
in the Mississippi Valley, and _Kessleria_ (later called
_Pseudoscaphirhynchus_), in Central Asia alone. Most of the species
belong to the genus _Acipenser_, which abounds in all the rivers and
seas in which salmon are found. Some of the smaller species spend their
lives in the rivers, ascending smaller streams to spawn. Other sturgeons
are marine, ascending fresh waters only for a moderate distance in the
spawning season. They range in length from 2½ to 30 feet.
All are used as food, although the flesh is rather coarse and beefy.
From their large size and abundance they possess great economic value.
The eggs of some species are prepared as caviar.
[Illustration:
FIG. 6.—Common Sturgeon, _Acipenser sturio_ Mitchill. Potomac River.
]
The sturgeons are sluggish, clumsy, bottom-feeding fish. The mouth,
underneath the long snout, is very protractile, sucker-like, and without
teeth. Before it on the under side of the snout are four long feelers.
Ordinarily the sturgeon feeds on mud and snails with other small
creatures, but I have seen large numbers of Eulachon (_Thaleichthys_) in
the stomach of the Columbia River sturgeon (_Acipenser transmontanus_).
This fish and the Eulachon run in the Columbia at the same time, and the
sucker-mouth of a large sturgeon will draw into it numbers of small
fishes who may be unsuspiciously engaged in depositing their spawn. In
the spawning season in June these clumsy fishes will often leap wholly
out of the water in their play. The sturgeons have a rough skin besides
five series of bony plates which change much with age and which in very
old examples are sometimes lost or absorbed in the skin. The common
sturgeon of the Atlantic on both shores is _Acipenser sturio_.
_Acipenser huso_ and numerous other species are found in Russia and
Siberia. The great sturgeon of the Columbia is _Acipenser
transmontanus_, and the great sturgeon of Japan _Acipenser kikuchii_.
Smaller species are found farther south, as in the Mediterranean and
along the Carolina coast. Other small species abound in rivers and
lakes. _Acipenser rubicundus_ is found throughout the Great Lake region
and the Mississippi Valley, never entering the sea. It is four to six
feet long, and at Sandusky, Ohio, in one season 14,000 sturgeons were
taken in the pound nets. A similar species, _Acipenser mikadoi_, is
abundant and valuable in the streams of northern Japan.
[Illustration:
FIG. 7.—Lake Sturgeon, _Acipenser rubicundus_ Le Sueur. Ecorse, Mich.
]
In the genus _Acipenser_ the snout is sharp and conical, and the
shark-like spiracle is still retained.
[Illustration:
FIG. 8.—Shovel-nosed Sturgeon. _Scaphirhynchus platyrhynchus_
(Rafinesque). Ohio River.
]
The shovel-nosed sturgeon (_Scaphirhynchus platyrhynchus_) has lost the
spiracles, the tail is more slender, its surface wholly bony, and the
snout is broad and shaped like a shovel. The single species of
_Scaphirhynchus_ abounds in the Mississippi Valley, a fish more
interesting to the naturalist than to the fisherman. It is the smallest
of our sturgeons, often taken in the nets in large numbers.
In _Scaphirhynchus_ the tail is covered by a continuous coat of mail. In
_Kessleria[6] fedtschenkoi_, _rossikowi_, and other Asiatic species the
tail is not mailed.
Footnote 6:
These species have also been named _Pseudoscaphirhynchus_. _Kessleria_
is the earlier name, left undefined by its describer, although the
type was indicated.
=Order Selachostomi: the Paddle-fishes.=—Another type of Ganoids, allied
to the sturgeons, perhaps still further degenerate, is that of the
paddle-fishes, called by Cope _Selachostomi_ (σέλαχος, shark; στόμα,
mouth). This group consists of a single family, _Polyodontidæ_, having
apparently little in common with the other Ganoids, and in appearance
still more suggestive of the sharks. The common name of paddle-fishes is
derived from the long flat blade in which the snout terminates. This
extends far beyond the mouth, is more or less sensitive, and is used to
stir up the mud in which are found the minute organisms on which the
fish feeds. Under the paddle are four very minute barbels corresponding
to those of the sturgeons. The vernacular names of spoonbill, duckbill
cat, and shovel-fish are also derived from the form of the snout. The
skin is nearly smooth, the tail is heterocercal, the teeth are very
small, and a long fleshy flap covers the gill-opening. The very long and
slender gill-rakers serve to strain the food (worms, leeches,
water-beetles, crustaceans, and algæ) from the muddy waters from which
they are taken. The most important part of this diet consists of
Entomostracans. The single American species, _Polyodon spathula_,
abounds through the Mississippi Valley in all the larger streams. It
reaches a length of three or four feet. It is often taken in the nets,
but the coarse tough flesh, like that of our inferior catfish, is not
much esteemed. In the great rivers of China, the Yangtse and the Hoang
Ho, is a second species, _Psephurus gladius_, with narrower snout, fewer
gill-rakers, and much coarser fulcra on the tail. The habits, so far as
known, are much the same.
[Illustration:
FIG. 9.—Paddle-fish, _Polyodon spathula_ (Walbaum). Ohio River.
]
[Illustration:
FIG. 10.—Paddle-fish. _Polyodon Spathula_ (Walbaum). Ohio River.
]
[Illustration:
FIG. 11.—_Psephurus gladius_ Günther. Yangtse River. (After Günther.)
]
_Crossopholis magnicaudatus_ of the Green River Eocene shales is a
primitive member of the _Polyodontidæ_. Its rostral blade is shorter
than that of _Polyodon_, and the body is covered with small thin scales,
each in the form of a small grooved disk with several posterior
denticulations, arranged in oblique series but not in contact. The
scales are quadrate in form, and more widely separated anteriorly than
posteriorly. As in _Polyodon_, the teeth are minute and there are no
branchiostegals. The squamation of this fish shows that _Polyodon_ as
well as _Acipenser_ may have sprung from a type having rhombic scales.
The tail of a Cretaceous fish, _Pholidurus disjectus_ from the
Cretaceous of Europe, has been referred with doubt to this family of
_Polyodontidæ_.
=Order Pycnodonti.=—In the extinct order _Pycnodonti_, as recognized by
Dr. O. P. Hay, the notochord is persistent and without ossification, the
body is very deep, the teeth are always blunt, the opercular apparatus
is reduced, the dorsal fin many-rayed, and the fins without fulcra. The
scales are rhombic, but are sometimes wanting, at least on the tail.
Many genera and species of _Pycnodontidæ_ are described, mostly from
Triassic and Jurassic rocks of Europe. Leading European genera are
_Pycnodus_, _Typodus_ (_Mesodon_), _Gyrodus_, and _Palæobalistum_. The
numerous American species belong to _Typodus_, _Cœlodus_, _Pycnodus_,
_Hadrodus_, and _Uranoplosus_. These forms have no affinity with
_Balistes_, although there is some resemblance in appearance, which has
suggested the name of _Palæobalistum_.
[Illustration:
FIG. 12.—_Gyrodus hexagonus_ Agassiz. Family _Pycnodontidæ_.
Lithographic Shales.
]
Woodward places these fishes with the _Semionotidæ_ and _Halecomorphi_
in his suborder of _Protospondyli_. It seems preferable, however, to
consider them as forming a distinct order.
[Illustration:
FIG. 13.—_Mesturus verrucosus_ Wagner. Family _Pycnodontidæ_. (After
Woodward.)
]
=Order Lepidostei.=—We may place, following Eastman's edition of Zittel,
the allies and predecessors of the garpike in a single order, for which
Huxley's name _Lepidostei_ may well be used. In this group the notochord
is persistent, and the vertebræ are in various degrees of ossification
and of different forms. The opercles are usually complete, the
branchiostegals present, and there is often a gular plate. There is no
infraclavicle and the jaws have sharp teeth. The fins have fulcra, and
the supports of the fins agree in number with the rays. The tail is more
or less heterocercal. The scales are rhombic, arranged in oblique
series, which are often united above and below with peg-and-socket
articulations. This group contains among recent fishes only the garpikes
(_Lepisosteus_). They are closely allied to the _Palæoniscidæ_, but the
skeleton is more highly ossified. On the other hand they approach very
closely to the ancestors of the bowfin, _Amia_. One genus,
_Acentrophorus_, appears in the Permian; the others are scattered
through Mesozoic and Tertiary rocks, the isolated group of gars still
persisting. In the gars the vertebræ are concavo-convex, with
ball-and-socket joints. In the others the vertebræ are incomplete or
else double-concave, as in fishes generally.
For the group here called _Lepidostei_ numerous other names have been
used corresponding wholly or in part. _Rhomboganoidea_ of Gill covers
nearly the same groups; _Holostei_ of Müller and _Hyoganoidea_ of Gill
include the _Halecomorphi_ also; _Ginglymodi_ of Cope includes the
garpikes only, while _Ætheospondyli_ of Woodward includes the
_Aspidorhynchidæ_ and the garpikes.
[Illustration:
FIG. 14.—_Semionotus kapffi_ Fraas, restored. Family _Semionotidæ_.
(After Fraas, per Nicholson.)
]
The _Semionotidæ_ (_Stylodontidæ_) are robust-bodied Ganoids, having the
vertebræ developed as rings, the jaws with several rows of teeth, those
of the outer row styliform.
_Semionotus bergeri_ is a well-known species, with the body moderately
elongate. _Semionotus agassizi_ and many other species occur in the
Triassic of the Connecticut valley and in New Jersey. The body is very
deep in the related genus _Dapedium_, and the head is covered with
strong bony plates. _Dapedium politum_ is a well-known species of the
English Triassic. _Tetragonolepis_ (_Pleurolepis_) is a similar form,
very deep and compressed, with strong, firm scales.
In the extinct family of _Lepidotidæ_ the teeth are conical or
chisel-shaped, while blunt or molar teeth are on the inside of the
mouth, which is small, and the suspensorium of the mandible is vertical
or inclined forward. The body is robust-fusiform, covered with rhomboid
scales; the vertebræ form rings about the notochord; the teeth are
either sharp or blunt. The dorsal fin is short, with large fulcra.
The best known of the numerous genera are _Lepidotes_, rather elongate
in body, with large, blunt teeth. Of the many species of _Lepidotes_,
_Lepidotes elvensis_ abounds in the English and German Triassic, and
_Lepidotes minor_ in the English Triassic. Another well-known European
species is _Lepidotes mantelli_.
[Illustration:
FIG. 15.—_Dapedium politum_ Leach, restored. Family _Semionotidæ_.
(After Woodward.)
]
The _Isopholidæ_ (_Eugnathidæ_) differ from the families last named in
the large pike-like mouth with strong teeth. The mandibular suspensorium
is inclined backwards. The body is elongate, the vertebræ forming
incomplete rings; the dorsal fin is short with large fulcra.
_Isopholis dentosus_ is found with numerous other species in the British
Triassic. _Caturus furcatus_ is especially characteristic of Triassic
rocks in Germany. _Ptycholepis marshi_ occurs in the Connecticut valley.
[Illustration:
FIG. 16.—_Tetragonolepis semicinctus_ Brown. Lias. Family
_Semionotidæ_. (After Woodward.)
]
The _Macrosemiidæ_ are elongate fishes with long dorsal fin, the
numerous species being found in the Triassic, Jurassic, and Cretaceous
of Europe. _Macrosemius rostratus_ has a very high, continuous dorsal.
_Macropistius arenatus_ is found in the Cretaceous of Texas, the only
American species known. Prominent European genera are _Notagogus_,
_Ophiopsis_, and _Petalopteryx_.
[Illustration:
FIG. 17.—_Isopholis orthostomus_ (Agassiz). Lias. (After Woodward.)
]
[Illustration:
FIG. 18.—The Long-nosed Garpike, _Lepisosteus osseus_ (Linnæus). Fox
River, Wisconsin. (From nature; D. S. Jordan and M. L. McDonald,
1874.)
]
Intermediate between the allies of the gars and the modern herrings is
the large extinct family of _Pholidophoridæ_, referred by Woodward to
the _Isospondyli_, and by Eastman to the _Lepidostei_. These are small
fishes, fusiform in shape, chiefly of the Triassic and Jurassic. The
fins are fringed with fulcra, the scales are ganoid and rhombic, and the
vertebræ reduced to rings. The mouth is large, with small teeth, and
formed as in the _Isospondyli_. The caudal is scarcely heterocercal.
[Illustration:
FIG. 19.—_Caturus elongatus_ Agassiz. Jurassic. Family _Isopholidæ_.
(After Zittel.)
]
[Illustration:
FIG. 20.—_Notagogus pentlandi_ Agassiz. Jurassic. Family
_Macrosemiidæ_. (After Woodward.)
]
[Illustration:
FIG. 21.—_Ptycholepis curtus_ Egerton. Lias. Family _Isopholidæ_.
(After Woodward.)
]
Of _Pholidophorus_, with scales joined by peg-and-socket joints and
uniform in size, there are many species. _Pholidophorus latiusculus_ and
many others are found in the Triassic of England and the Continent.
_Pholidophorus americanus_ occurs in the Jurassic of South Dakota.
_Pleuropholis_, with the scales on the lateral line, which runs very
low, excessively deepened, is also widely distributed. I have before me
a new species from the Cretaceous rocks near Los Angeles. The
_Archæomænidæ_ differ from _Pholidophoridæ_ in having cycloid scales. In
both families the vertebræ are reduced to rings about the notochord.
From fishes allied to the _Pholidophoridæ_ the earliest _Isospondyli_
are probably descended.
[Illustration:
FIG. 22.—_Pholidophorus crenulatus_ Egerton. Lias. (After Woodward.)
]
In the _Aspidorhynchidæ_ the snout is more or less produced, the
mandible has a distinct presymphysial bone, the vertebræ are
double-concave or ring-like, and the fins are without fulcra. This
family constitutes the suborder _Ætheospondyli_. In form these fishes
resemble _Albula_ and other modern types, but have mailed heads and an
ancient type of scales. Two genera are well known, _Aspidorhynchus_ and
_Belonostomus_. _Aspidorhynchus acutirostris_ reaches a length of three
feet, and is found in the Triassic lithographic stone of Bavaria. Other
species occur in rocks of Germany and England.
_Belonostomus_ has the snout scarcely produced. _Belonostomus
sphyrænoides_ is the best known of the numerous species, all of the
Triassic, Jurassic, and Cretaceous.
=Family Lepisosteidæ.=—The family of _Lepisosteidæ_, constituting the
suborder _Ginglymodi_ (γιγγλυμός, hinge), is characterized especially by
the form of the vertebræ.
These are opisthocœlian, convex in front and concave behind, as in
reptiles, being connected by ball-and-socket joints. The tail is
moderately heterocercal, less so than in the _Halecomorphi_, and the
body is covered with very hard, diamond-shaped, enameled scales in
structure similar to that of the teeth. A number of peculiar characters
are shown by these fishes, some of them having often been regarded as
reptilian traits. Notable features are the elongate, crocodile-like
jaws, the upper the longer, and both armed with strong teeth. The
mandible is without presymphysial bone. The fins are small with large
fulcra, and the scales are nearly uniform in size.
All the species belong to a single family, _Lepisosteidæ_, which
includes the modern garpikes and their immediate relatives, some of
which occur in the early Tertiary. These voracious fishes are
characterized by long and slender cylindrical bodies, with enameled
scales and mailed heads and heterocercal tail. The teeth are sharp and
unequal. The skeleton is well ossified, and the animal itself is
extremely voracious. The vertebræ, reptile-like, are opisthocœlian, that
is, convex in front, concave behind, forming ball-and-socket joints. In
almost all other fishes they are amphicœlian or double-concave, the
interspace filled with gelatinous substance. The recent species, and
perhaps all the extinct species also, belong to the single genus
_Lepisosteus_ (more correctly, but also more recently, spelled
_Lepidosteus_). Of existing forms there are not many species, three to
five at the most, and they swarm in the lakes, bayous, and sluggish
streams from Lake Champlain to Cuba and along the coast to Central
America. The best known of the species is the long-nosed garpike,
_Lepisosteus osseus_, which is found throughout most of the Great Lake
region and the Mississippi Valley, and in which the long and slender
jaws are much longer than the rest of the head. The garpike frequents
quiet waters and is apparently of sleepy habit. It often lies quiet for
a long time, carried around and around by the eddies. It does not
readily take the hook and seldom feeds in the aquarium. It feeds on
crayfishes and small fishes, to which it is exceedingly destructive, as
its bad reputation indicates. Fishermen everywhere destroy it without
mercy. Its flesh is rank and tough and unfit even for dogs.
In the young garpike the caudal fin appears as a second dorsal and anal,
the filamentous tip of the tail passing through and beyond it.
The short-nosed garpike, _Lepisosteus platystomus_, is generally common
throughout the Mississippi Valley. It has a short broad snout like the
alligator-gar, but seldom exceeds three feet in length. In size, color,
and habits it agrees closely with the common gar, differing only in the
form of the snout. The form is subject to much variation, and it is
possible that two or more species have been confounded.
[Illustration:
FIG. 23.—Alligator-gar, _Lepisosteus tristœchus_ (Bloch). Cuba.
]
The great alligator-gar, _Lepisosteus tristœchus_, reaches a length of
twenty feet or more, and is a notable inhabitant of the streams about
the Gulf of Mexico. Its snout is broad and relatively wide, and its
teeth are very strong. It is very destructive to all sorts of
food-fishes. Its flesh is worthless, and its enameled scales resist a
spear or sometimes even shot. It breathes air to a certain extent by its
lungs, but soon dies in foul water, not having the tenacity of life seen
in _Amia_.
=Embryology of the Garpike.=—Mr. Alexander Agassiz has given an account
of the embryology of the garpike, of which the following is an abstract:
"The garpike comes up the St. Lawrence in May, lays its eggs about the
20th, and then disappears. The eggs are large, viscous, stick fast in an
isolated way to whatever they fall upon, and look much like those of
toads, having a large outer membrane and a small yolk. Artificial
fecundation failed, but about 500 naturally-laid eggs were secured, of
which all but 30 perished through mold. The young began to hatch in six
days. Out of 30 young hatched, 27 lived until the 15th of July.
Connection with the sharks appears in the similarity of the branchial
arches and by the presence of the lateral fold in which the pectoral
fins are formed; the way the tail is developed is very like that of the
bony fishes. Among the Ganoids it appears, as well as in ordinary
fishes, the dorsal cord is straight at first, then assumes a slightly
upward curve at the extremity, when finally there appears the beginning
of a lobe underneath, pointing to a complete heterocercal tail. All this
is as in the bony fishes, but this is the permanent condition of the
garpike, while in the bony fishes the extremity of the dorsal cord
becomes extinct. The mode of development of the pectoral lobe (very
large in this species) furnishes another resemblance. In the brain, and
in the mode of formation of the gills, a likeness to the sharks is
noticeable. The young garpikes move very slowly, and seem to float
quietly, save an exceedingly rapid vibration of the pectorals and the
tip of the tail. They do not swim about much, but attach themselves to
fixed objects by an extraordinary horseshoe-shaped ring of
sucker-appendages about the mouth. These appendages remain even after
the snout has become so extended that the ultimate shape is hinted at;
and furthermore, it is a remnant of this feature that forms the fleshy
bulb at the end of the snout in the adult. The investigations thus far
show that the young garpike has many characteristics in common with the
sharks and skates, but it is not so different from the bony fishes as
has been supposed."
=Fossil Garpikes.=—A number of fossil garpikes, referred by Cope to the
genus _Clastes_ and by Eastman and Woodward to _Lepidosteus_, are found
in the Eocene of Europe and America. The most perfect of these remains
is called _Lepisosteus atrox_, upward of four feet long, as large as an
alligator-gar, which the species much resembles. Although found in the
Eocene, Dr. C. R. Eastman declares that "it has no positively archaic
features. If we inquire into the more remote or pre-Eocene history of
Lepidosteids, palæontology gives no answer. They blossom forth suddenly
and fully differentiated at the dawn of the Tertiary, without the least
clue to their ancestry, unheralded and unaccompanied by any intermediate
forms, and they have remained essentially unchanged ever since."
Another fossil species is _Lepisosteus fimbriatus_, from the Upper
Eocene of England. Scales and other fragments of garpikes are found in
Germany, Belgium, and France, in Eocene and Miocene rocks. On some of
these the nominal genera _Naisia_, _Trichiurides_, and _Pneumatosteus_
are founded. _Clastes_, regarded by Eastman as fully identical with
_Lepisosteus_, is said to have the "mandibular ramus without or with a
reduced fissure of the dental foramen, and without the groove continuous
with it in _Lepisosteus_. One series of large teeth, with small ones
external to them on the dentary bone." Most of the fossil forms belong
to _Clastes_, but the genus shows no difference of importance which will
distinguish it from the ordinary garpike.
[Illustration:
FIG. 24.—Lower jaw of _Amia calva_ Linnæus, showing the gular plate.
]
=Order Halecomorphi.=—To this order belong the allies, living or
extinct, of the bowfin (_Amia_), having for the most part cycloid scales
and vertebræ approaching those of ordinary fishes. The resemblance to
the _Isospondyli_, or herring group, is indicated in the name (Halec, a
herring; μορφή, form). The notochord is persistent, the vertebræ
variously ossified. The opercles are always complete. The
branchiostegals are broad and there is always a gular plate. The teeth
are pointed, usually strong. There is no infraclavicle. Fulcra are
present or absent. The supports of the dorsal and anal are equal in
number to the rays. Tail heterocercal. Scales thin, mostly cycloid, but
bony at base, not jointed with each other. Mandible complex, with
well-developed splenial rising into a coronoid process, which is
completed by a distinct coronoid bone. Pectoral fin with more than five
actinosts; scales ganoid or cycloid. In the living forms the air-bladder
is connected with the œsophagus through life; optic chiasma present;
intestine with a spiral valve. This group corresponds to the _Amioidei_
of Lütken and essentially to the _Cycloganoidei_ of Gill. The
_Protospondyli_ (προτός, before; σπόνδυλος, vertebra) of Woodward
contains essentially the same elements.
=Pachycormidæ.=—In the family of _Pachycormidæ_ the notochord is
persistent, the ethmoids and vomer fused and projecting between the
maxillaries to form the prominent snout, the teeth large, the body
fusiform, the dorsal short, with slender rays and few fulcra or none,
and the scales are thin and rhombic. The numerous species are
characteristic of the Triassic, Jurassic, and Cretaceous. In _Sauropsis_
(_longimana_) the body is elongate, and the pectoral fins are large and
sickle-shaped. _Euthynotus_ has small fulcra. In _Pachycormus_
(_macropterus_, _esocinus_, etc.) the form is robust and the ventral
fins are wanting. In _Hypsycormus_ ventrals are present, and the caudal
deeply forked.
In the American family of _Protosphyrænidæ_ the jaws are armed with very
strong teeth, as in the Barracuda, which, however, the species do not
resemble in other respects. _Protosphyræna nitida_, _perniciosa_, and
numerous other extinct forms, some of them of large size, were voracious
inhabitants of the Cretaceous seas, and are found fossil, especially in
North Carolina and Kansas. Numerous species called _Erisichthe_ and
_Pelecopterus_ are all referred by Hay to _Protosphyræna_. In this
family the scapula and coracoids are ossified, and perhaps the vertebræ
also, and, as Dr. Hay has recently suggested, the _Protosphyrænidæ_ may
really belong to the _Isospondyli_. In any event, they stand on the
border-line between the most fish-like of the Ganoids and the most
archaic of the bony fishes.
The _Liodesmidæ_ (genus _Liodesmus_) are much like _Amia_, but the
notochord is persistent, its sheath without ossification. _Liodesmus
gracilis_ and _L. sprattiformis_ occur in the lithographic stones of
Bavaria. Woodward places _Liodesmus_ with _Megalurus_ among the
_Amiidæ_.
=The Bowfins: Amiidæ.=—The _Amiidæ_ have the vertebræ more complete. The
dorsal fin is many-rayed and is without distinct fulcra. The
diamond-shaped enameled scales disappear, giving place to cycloid
scales, which gradually become thin and membranous in structure. A
median gular plate is developed between the branchiostegals. The tail is
moderately heterocercal, and the head covered with a bony coat of mail.
The family of _Amiidæ_ contains a single recent species, _Amia calva_,
the only living member of the order _Halecomorphi_. The bowfin, or
grindle, is a remarkable fish abounding in the lakes and swamps of the
Mississippi Valley, the Great Lake region, and southward to Virginia,
where it is known by the imposing but unexplained title of John A.
Grindle. In the Great Lakes it is usually called "dogfish," because even
the dogs will not eat it, and "lawyer," because, according to Dr.
Kirtland, "it will bite at anything and is good for nothing when
caught."
The bowfin reaches a length of two and one half feet, the male being
smaller than the female and marked by an ocellated black spot on the
tail. Both sexes are dark mottled green in color. The flesh of the
species is very watery, pasty, much of the substance evaporating when
exposed to the air. It is ill-flavored, and is not often used as food.
The species is very voracious and extremely tenacious of life. Its
well-developed lung enables it to breathe even when out of the water,
and it will live in the air longer than any other fish of American
waters, longer even than the horned pout (_Ameiurus_) or the mud-minnow
(_Umbra_). As a game fish the grindle is one of the very best, if the
angler does not care for the flesh of what he catches, it being one of
the hardest fighters that ever took the hook.
[Illustration:
FIG. 25.—Bowfin (female), _Amia calva_ Linnæus. Lake Michigan.
]
The _Amiidæ_ retain many of the Ganoid characters, though approaching
more nearly than any other of the Ganoids to the modern herring tribe.
For this reason the name _Halecomorphi_ (shad-formed) was given to this
order by Professor Cope. The gular plate found in Amia and other Ganoids
reappears in the herring-like family of _Elopidæ_, which includes the
tarpon and the ten-pounder.
Woodward unites the extinct genera called _Cyclurus_, _Notæus_,
_Amiopsis_, _Protamia_, _Hypamia_, and _Pappichthys_ with _Amia_.
_Pappichthys_ (_corsoni_, etc.), from the Wyoming Eocene, is doubtless a
valid genus, having but one row of teeth in each jaw, and _Amiopsis_ is
also recognized by Hay. Woodward refers to _Amia_ the following extinct
species: _Amia valenciennesi_, from the Miocene of France; _Amia
macrocephala_, from the Miocene of Bohemia; and _Amia ignota_, from the
Eocene of Paris. Other species of Amia are known from fragments. Several
of these are from the Eocene of Wyoming and Colorado. Some of them have
a much shorter dorsal fin than that of _Amia calva_ and may be
generically different.
[Illustration:
FIG. 26.—_Megalurus elegantissimus_ Wagner. Family _Amiidæ_. (After
Zittel.)
]
The genus _Megalurus_ differs from _Amia_ in the still shorter dorsal
fin, less than one-third the length of the back. The body is elongate
and much depressed. _Megalurus lepidotus_ and several other species are
found in the lithographic stones of Bavaria and elsewhere.
=The Oligopleuridæ.=—In the extinct family _Oligopleuridæ_ the scales
are cycloid, the bones of the head scarcely enameled, and the vertebræ
well ossified. Fulcra are present, and the mouth is large, with small
teeth. The genera are _Oligopleurus_, _Ionoscopus_, and _Spathiurus_,
the species not very numerous and chiefly of the Cretaceous. _Ionoscopus
cyprinoides_ of the lithographic shales of Bavaria is a characteristic
species.
From the three families last named, with the _Pholidophoridæ_, there is
an almost perfect transition from the Ganoid fishes to teleosteans of
the order of _Isospondyli_, the primitive order from which all other
bony fishes are perhaps descended. The family of _Leptolepidæ_,
differing from _Oligopleuridæ_ in the absence of fulcra, is here placed
with the _Isospondyli_, but it might about as well be regarded as
Ganoid.