THE TRUE SHARKS
=Order Notidani.=--We may recognize as a distinct order, a primitive
group of recent sharks, a group of forms finding its natural place
somewhere between the _Cladoselachidæ_ and _Heterodontidæ_, both of
which groups long preceded it in geological time.
The name _Notidani_ (_Notidanus_, ~nôtidanos~, dry back, an old name of
one of the genera) may be retained for this group, which corresponds
to the _Diplospondyli_ of Hasse, the _Opistharthri_ of Gill, and the
_Protoselachii_ of Parker and Haswell. The _Notidani_ are characterized
by the primitive structure of the spinal column, which is without
calcareous matter, the centra being imperfectly developed. There
are six or seven branchial arches, and in the typical forms (not in
_Chlamydoselachus_) the palato-quadrate or upper jaw articulates
with the postorbital region of the skull. The teeth are of primitive
character, of different forms in the same jaw, each with many cusps.
The fins are without spines, the pectoral fin having the three basal
cartilages (mesopterygium with propterygium and metapterygium) as usual
among sharks.
[Illustration: FIG. 312.--Griset or Cow-shark, _Hexanchus griseus_
(Gmelin). Currituck Inlet, N. C.]
The few living forms are of high interest. The extinct species are
numerous, but not very different from the living species.
=Family Hexanchidæ.=--The majority of the living Notidanoid sharks
belong to the family of _Hexanchidæ_. These sharks have six or seven
gill-openings, one dorsal fin, and a relatively simple organization.
The bodies are moderately elongate, not eel-shaped, and the
palato-quadrate articulates with the postorbital part of the skull.
The six or eight species are found sparsely in the warm seas. The two
genera, _Hexanchus_, with six, and _Heptranchias_, with seven vertebræ,
are found in the Mediterranean. The European species are _Hexanchus
griseus_, the cow-shark, and _Heptranchias cinereus_. The former
crosses to the West Indies. In California, _Heptranchias maculatus_
and _Hexanchus corinus_ are occasionally taken, while _Heptranchias
deani_ is the well known Aburazame or oil shark of Japan. _Heptranchias
indicus_, a similar species, is found in India.
[Illustration: FIG. 313.--Teeth of _Heptranchias indicus_ Gmelin.]
Fossil _Hexanchidæ_ exist in large numbers, all of them referred
by Woodward to the genus _Notidanus_ (which is a later name than
_Hexanchus_ and _Heptranchias_ and intended to include both these
genera), differing chiefly in the number of gill-openings, a character
not ascertainable in the fossils. None of these, however, appear before
Cretaceous time, a fact which may indicate that the simplicity of
structure in _Hexanchus_ and _Heptranchias_ is a result of degeneration
and not altogether a mark of primitive simplicity. The group is
apparently much younger than the Cestraciontes and little older than
the Lamnoids, or the Squaloid groups. _Heptranchias microdon_ is common
in English Cretaceous rocks, and _Heptranchias primigenius_ and other
species are found in the Eocene.
=Family Chlamydoselachidæ.=--Very great interest is attached
to the recent discovery by Samuel Garman of the frilled shark,
_Chlamydoselachus anguineus_, the sole living representative of the
_Chlamydoselachidæ_.
[Illustration: FIG. 314.--Frill-shark, _Chlamydoselachus anguineus_
Garman. From Misaki, Japan. (After Günther.)]
This shark was first found on the coast of Japan, where it is rather
common in deep water. It has since been taken off Madeira and off
the coast of Norway. It is a long, slender, eel-shaped shark with
six gill-openings and the palato-quadrate not articulated to the
cranium. The notochord is mainly persistent, in part replaced
by feeble cyclospondylic vertebral centra. Each gill-opening is
bordered by a broad frill of skin. There is but one dorsal fin. The
teeth closely resemble those of _Dittodus_ or _Didymodus_ and other
extinct _Ichthyotomi_. The teeth have broad, backwardly extended
bases overlapping, the crown consisting of three slender curved
cusps, separated by rudimentary denticles. Teeth of a fossil species,
_Chlamydoselachus lawleyi_, are recorded by J. W. Davis from the
Pliocene of Tuscany.
=Order Asterospondyli.=--The order of _Asterospondyli_ comprises
the typical sharks, those in which the individual vertebræ are
well developed, the calcareous lamellæ arranged so as to radiate,
star-fashion, from the central axis. All these sharks possess two
dorsal fins and one anal fin, the pectoral fin is normally developed,
with the three basal cartilages; there are five gill-openings, and the
tail is heterocercal.
[Illustration: FIG. 315.--Bullhead-shark, _Heterodontus francisci_
(Girard). San Pedro, Cal.]
=Suborder Cestraciontes.=--The most ancient types may be set off as a
distinct suborder under the name of _Cestraciontes_ or _Prosarthri_.
[Illustration: FIG. 316.--Lower jaw of _Heterodontus philippi_. From
Australia. Family _Heterodontidæ_. (After Zittel.)]
These forms find their nearest allies in the _Notidani_, which they
resemble to some extent in dentition and in having the palato-quadrate
articulated to the skull although fastened farther forward than in the
_Notidani_. Each of the two dorsal fins has a strong spine.
[Illustration: FIG. 317.--Teeth of Cestraciont Sharks. (After
Woodward.) _d_, _Synechodus dubrisianus_ Mackie; _e_, _Heterodontus
canaliculatus_ Egerton; _f_, _Hybodus striatulus_ Agassiz. (After
Woodward.)]
[Illustration: FIG. 318.--Egg of Port Jackson Shark, _Heterodontus
philippi_ (Lacépède). (After Parker & Haswell.)]
=Family Heterodontidæ.=--Among recent species this group contains only
the family of _Heterodontidæ_, the bullhead sharks, or Port Jackson
sharks. In this family the head is high, with usually projecting
eyebrows, the lateral teeth are pad-like, ridged or rounded, arranged
in many rows, different from the pointed anterior teeth, the fins are
large, the coloration is strongly marked, and the large egg-cases are
spirally twisted. All have five gill-openings. The living species
of _Heterodontidæ_ are found only in the Pacific, the Port Jackson
shark of Australia, _Heterodontus philippi_, being longest known.
Other species are _Heterodontus francisci_, common in California,
_Heterodontus japonicus_, in Japan, and _Heterodontus zebra_, in China.
These small and harmless sharks at once attract attention by their
peculiar forms. In the American species the jaws are less contracted
than in the Asiatic species, called _Heterodontus_. For this reason Dr.
Gill has separated the former under the name of _Gyropleurodus_. The
differences are, however, of slight value. The genus _Heterodontus_
first appears in the Jurassic, where a number of species are known, one
of the earliest being _Heterodontus falcifer_.
Three families of _Cestraciontes_ are recognized by Hay. The most
primitive of these is the group of _Orodontidæ_. _Orodus_, from the
Lower Carboniferous, has the teeth with a central crown, its surface
wrinkled. Of the _Heterodontidæ_, _Hybodus_, of the Carboniferous and
Triassic, is one of the earliest and largest genera, characterized
by elongate teeth of many cusps, different in different parts of
the jaw, somewhat as in the _Hexanchidæ_, the median points being,
however, always longest. The dorsal fins are provided with long spines
serrated behind. The vertebræ with persistent notochord show qualities
intermediate between those of _Hexanchidæ_ and _Heterodontidæ_, and the
same relation is shown by the teeth. In this genus two large hooked
half-barbed dermal spines occur behind each orbit.
[Illustration: FIG. 319.--Tooth of _Hybodus delabechei_ Charlesworth.
(After Woodward.)]
[Illustration: FIG. 320.--Fin-spine of _Hybodus basanus_ Egerton.
Cretaceous. Family _Heterodontidæ_. (After Nicholson.)]
[Illustration: FIG. 321.--Fin-spine of _Hybodus reticulatus_ Agassiz.
(After Zittel.)]
_Palæospinax_, with short stout spines and very large pectoral fins,
formerly regarded as a dogfish, is placed near _Heterodontus_ by
Woodward. _Acrodus_, from the Triassic, shows considerable resemblance
to _Heterodontus_. Its teeth are rounded and without cusps.
Most of these species belong to the Carboniferous, Triassic, and
Jurassic, although some fragments ascribed to Cestraciont sharks occur
in the Upper Silurian. _Asteracanthus_, known only from fin-spines in
the Jura, probably belongs here.
It is a singular fact first noted by Dr. Hay, that with all the
great variety of sharks, ten families in the Carboniferous age,
representatives of but one family, _Heterodontidæ_, are found in the
Triassic. This family may be the parent of all subsequent sharks and
rays, six families of these appearing in the Jurassic and many more in
the Cretaceous.
=Edestus and its Allies.=--Certain monstrous structures, hitherto
thought to be fin-spines, are now shown by Dr. Eastman and others to be
coalescent teeth of Cestraciont sharks.
[Illustration: Fig. 322.--Fin-spine of _Hybodus canaliculatus_ Agassiz.]
[Illustration: Fig. 323.--Teeth of Cestraciont Sharks. (After
Woodward.) _a_, _Hybodus lævis_ Woodward (after Woodward); _b_,
_Heterodontus rugosus_ Agassiz; _c_, _Hybodus delabechei_ Charlesworth.]
[Illustration: Fig. 324.--_Edestus vorax_ Leidig, supposed to be a
whorl of teeth. (After Newberry.)]
These remarkable _Ichthyodorulites_ are characteristic structures of
sharks of unknown nature, but probably related to the _Heterodontidæ_.
Of these the principal genera are _Edestus_, _Helicoprion_, and
_Campyloprion_. Karpinsky regards these ornate serrated spiral
structures as whorls of unshed teeth cemented together and extending
outside the mouth, "sharp, piercing teeth which were never shed but
became fused in whorls as the animals grew."
Dr. Eastman has, however, shown that these supposed teeth of _Edestus_
are much like those of the _Cochliodontidæ_, and the animals which bore
them should doubtless find their place among the Cestraciont sharks,
perhaps within the family of _Heterodontidæ_.
[Illustration: FIG. 325.--_Helicoprion bessonowi_ Karpinsky. Teeth from
the Permian of Krasnoufimsk, Russia. (After Karpinsky.)]
=Onchus.=--The name _Onchus_ was applied by Agassiz to small laterally
compressed spines, their sides ornamented with smooth or faintly
crenulated longitudinal ridges, and with no denticles behind.
Very likely these belonged to extinct Cestraciont sharks. _Onchus
murchisoni_ and _Onchus tenuistriatus_ occur in the Upper Silurian
rocks of England, in the lowest strata in which sharks have been found.
To a hypothetical group of primitive sharks Dr. Hasse has given the
name of _Polyospondyli_. In these supposed ancestral sharks the
vertebræ were without any ossification, a simple notochord, possibly
swollen at intervals. The dorsal fin was single and long, a fold of
skin with perhaps a single spine as an anterior support. The teeth
must have been modified dermal papillæ, each probably with many
cusps. Probably seven gill-openings were developed, and the tail was
diphycercal, ending in a straight point. The finely striated fin-spines
not curved upward at tip, called _Onchus_ from the Upper Silurian of
the Ludlow shales of England and elsewhere, are placed by Hasse near
his Polyspondylous sharks. Such spines have been retained by the group
of _Chimæras_, supposed to be derived from the ancestors of _Onchus_,
as well as by the _Heterodontidæ_ and _Squalidæ_.
=Family Cochliodontidæ.=--Another ancient family known from teeth
alone is that of _Cochliodontidæ_. These teeth resemble those of
the _Heterodontidæ_, but are more highly specialized. The form of
the body is unknown, and the animals may have been rays rather than
sharks. Eastman leaves them near the _Petalodontidæ_, which group
of supposed rays shows a similar dentition. The teeth are convex in
form, strongly arched, hollowed at base, and often marked by ridges or
folds, being without sharp cusps. In each jaw is a strong posterior
tooth with smaller teeth about. The elaborate specialization of these
ancient teeth for crushing or grinding shells is very remarkable.
The species are chiefly confined to rocks of the Carboniferous age.
Among the principal genera are _Helodus_, _Psephodus_, _Sandalodus_,
_Venustodus_, _Xystrodus_, _Deltodus_, _Poecilodus_, and _Cochliodus_.
[Illustration: FIG. 326.--Lower jaw of _Cochliodus contortus_ Agassiz.
Carboniferous. (After Zittel.)]
Concerning the teeth of various fossil sharks, Dr. Dean observes:
"Their general character appears to have been primitive, but in
structural details they were certainly specialized. Thus their
dentition had become adapted to a shellfish diet, and they had evolved
defensive spines at the fin margins, sometimes at the sides of the
head. In some cases the teeth remain as primitive shagreen cusps on
the rim of the mouth, but become heavy and bluntish behind; in other
forms the fusion of tooth clusters may present the widest range in
their adaptations for crushing; and the curves and twistings of the
tritoral surfaces may have resulted in the most specialized forms of
dentition which are known to occur, not merely in sharks but among all
vertebrates."
In this neighborhood belongs, perhaps, the family of _Tamiobatidæ_,
known from the skull of a single specimen, called _Tamiobatis
vetustus_, from the Devonian in eastern Kentucky. The head has the
depressed form of a ray, but it is probably a shark and one of the very
earliest known.
=Suborder Galei.=--The great body of recent sharks belong to
the suborder _Galei_, or _Euselachii_, characterized by the
asterospondylous vertebræ, each having a star-shaped nucleus, and
by the fact that the palato-quadrate apparatus or upper jaw is not
articulated with the skull. The sharks of this suborder are the most
highly specialized of the group, the strongest and largest and, in
general, the most active and voracious. They are of three types
and naturally group themselves about the three central families
_Scyliorhinidæ_, _Lamnidæ_, and _Carchariidæ_ (_Galeorhinidæ_).
The _Asterospondyli_ are less ancient than the preceding groups, but
the modern families were well differentiated in Mesozoic times.
Among the _Galei_ the dentition is less complex than with the ancient
forms, although the individual teeth are more highly specialized. The
teeth are usually adapted for biting, often with knife-like or serrated
edges; only the outer teeth are in function; as they are gradually
lost, the inner teeth are moved outward, gradually taking the place of
these.
We may place first, as most primitive, the forms without nictitating
membrane.
=Family Scyliorhinidæ.=--The most primitive of the modern families
is doubtless that of the _Scyliorhinidæ_, or cat-sharks. This group
includes sharks with the dorsal fins both behind the ventrals, the tail
not keeled and not bent upward, the spiracles present, and the teeth
small and close-set. The species are small and mostly spotted, found
in the warm seas. All of them lay their eggs in large cases, oblong,
and with long filaments or strings at the corners. The cat-sharks, or
roussettes, _Scyliorhinus canicula_ and _Catulus stellaris_, abound
in the Mediterranean. Their skin is used as shagreen or sandpaper in
polishing furniture. The species of swell-sharks (_Cephaloscylium_)
(_C. uter_, in California; _C. ventriosus_, in Chile; _C. laticeps_,
in Australia; _C. umbratile_, in Japan) are short, wide-bodied sharks,
which have the habit of filling the capacious stomach with air, then
floating belly upward like a globefish. Other species are found in the
depths of the sea. _Scyliorhinus_, _Catulus_, and numerous other genera
are found fossil. The earliest is _Palæoscyllium_, in the Jurassic, not
very different from _Scyliorhinus_, but the fins are described as more
nearly like those of _Ginglymostoma_.
Close to the _Scyliorhinidæ_ is the Asiatic family, _Hemiscylliidæ_,
which differs in being ovoviviparous, the young, according to Mr.
Edgar R. Waite, hatched within the body. The general appearance is
that of the _Scyliorhinidæ_, the body being elongate. _Chiloscyllium_
is a well-known genus with several species in the East Indies.
_Chiloscyllium modestum_ is the dogfish of the Australian fishermen.
The _Orectolobidæ_ are thick-set sharks, with large heads provided with
fleshy fringes. _Orectolobus barbatus_ (_Crossorhinus_ of authors)
abounds from Japan to Australia.
Another family, _Ginglymostomidæ_, differs mainly in the form of
the tail, which is long and bent abruptly upward at its base. These
large sharks, known as nurse-sharks, are found in the warm seas.
_Ginglymostoma cirrhatum_ is the common species with _Orectolobus_.
_Stegostoma tigrinum_, of the Indian seas and north to Japan, one of
several genera called tiger-sharks, is remarkable for its handsome
spotted coloration. The extinct genus _Pseudogaleus_ (_voltai_) is said
to connect the _Scyliorhinoid_ with the _Carcharioid_ sharks.
=The Lamnoid or Mackerel Sharks.=--The most active and most ferocious
of the sharks, as well as the largest and some of the most sluggish,
belong to a group of families known collectively as Lamnoid, because
of a general resemblance to the mackerel-shark, or _Lamna_, as
distinguished from the blue sharks and white sharks allied to
_Carcharias_ (_Carcharhinus_).
The Lamnoid sharks agree with the cat-sharks in the absence of
nictitating membrane or third eyelid, but differ in the anterior
insertion of the first dorsal fin, which is before the ventrals. Some
of these sharks have the most highly specialized teeth to be found
among fishes, most effective as knives or as scissors. Still others
have the most highly specialized tails, either long and flail-like, or
short, broad, and muscular, fitting the animal for swifter progression
than is possible for any other sharks. The Lamnoid families are
especially numerous as fossils, their teeth abounding in all suitable
rock deposits from Mesozoic times till now. Among the Lamnoid sharks
numerous families must be recognized.
The most primitive is perhaps that of the _Odontaspididæ_ (called
_Carchariidæ_ by some recent authors), now chiefly extinct, with the
tail unequal and not keeled, and the teeth slender and sharp, often
with smaller cusps at their base. _Odontaspis_ and its relatives of the
same genus are numerous, from the Cretaceous onward, and three species
are still extant, small sharks of a voracious habit, living on sandy
shores. _Odontaspis littoralis_ (also known as _Carcharias littoralis_)
is the common sand-shark of our Atlantic coast. _Odontaspis taurus_ is
a similar form in the Mediterranean.
=Family Mitsukurinidæ, the Goblin-sharks.=--Closely allied to
_Odontaspis_ is the small family of _Mitsukurinidæ_, of which a single
living species is known. The teeth are like those of _Odontaspis_, but
the appearance is very different.
The goblin-shark, or Tenguzame, _Mitsukurina owstoni_, is a very large
shark rarely taken in the Kuro Shiwo, or warm "Black Current" of Japan.
It is characterized by the development of the snout into a long flat
blade, extending far beyond the mouth, much as in _Polyodon_ and in
certain Chimæras. Several specimens are now known, all taken by Capt.
Alan Owston of Yokohama in Sagami Bay, Japan. The original specimen,
a young shark just born, was presented by him to Professor Kakichi
Mitsukuri of the University of Tokyo. From this our figure was taken.
The largest specimen now known is in the United States National Museum
and is fourteen feet in length. In the Upper Cretaceous is a very
similar genus, _Scapanorhynchus_ (_lewisi_, etc.), which Professor
Woodward thinks may be even generically identical with _Mitsukurina_,
though there is considerable difference in the form of the still longer
rostral plate, and the species of _Scapanorhynchus_ differ among
themselves in this regard.
[Illustration: FIG. 327.--Goblin-shark (Tenguzame), _Mitsukurina
owstoni_ Jordan. From a young specimen in the Imperial University of
Tokyo.]
_Mitsukurina_, with _Heterodontus_, _Heptranchias_, and
_Chlamydoselache_, is a very remarkable survival of a very ancient
form. It is an interesting fact that the center of abundance of all
these relics of ancient life is in the Black Current, or Gulf Stream,
of Japan.
[Illustration: FIG. 328.--_Scapanorhynchus lewisi_ Davis. Family
_Mitsukurinidæ_. Under side of snout. (After Woodward.)]
=Family Alopiidæ, or Thresher Sharks.=--The related family of
_Alopiidæ_ contains probably but one recent species, the great
fox-shark, or thresher, found in all warm seas. In this species,
_Alopias vulpes_, the tail is as long as the rest of the body and bent
upward from the base. The snout is very short, and the teeth are small
and close-set. The species reaches a length of about twenty-five feet.
It is not especially ferocious, and the current stories of its attacks
on whales probably arise from a mistake of the observers, who have
taken the great killer, _Orca_, for a shark. The killer is a mammal,
allied to the porpoise. It attacks the whale with great ferocity,
clinging to its flesh by its strong teeth. The whale rolls over and
over, throwing the killer into the air, and sailors report it as a
thresher. As a matter of fact the thresher very rarely if ever attacks
any animal except small fish. It is said to use its tail in rounding
up and destroying schools of herring and sardines. Fossil teeth of
thresher-sharks of some species are found from the Miocene.
=Family Pseudotriakidæ.=--The _Pseudotriakidæ_ consist of two species.
One of these is _Pseudotriakis microdon_, a large shark with a long
low tail, long and low dorsal fin, and small teeth. It has been only
twice taken, off Portugal and off Long Island. The other, the mute
shark, _Pseudotriakis acrales_, a large shark with the body as soft as
a rag, is in the museum of Stanford University, having been taken by
Mr. Owston off Misaki.
=Family Lamnidæ.=--To the family of _Lamnidæ_ proper belong the
swiftest, strongest, and most voracious of all sharks. The chief
distinction lies in the lunate tail, which has a keel on either side
at base, as in the mackerels. This form is especially favorable
for swift swimming, and it has been independently developed in the
mackerel-sharks, as in the mackerels, in the interest of speed in
movement.
[Illustration: FIG. 329.--Tooth of _Lamna cuspidata_ Agassiz.
Oligocene. Family _Lamnidæ_. (After Nicholson.)]
The porbeagle, _Lamna cornubica_, known as salmon-shark in Alaska,
has long been noted for its murderous voracity. About Kadiak Island
it destroys schools of salmon, and along the coasts of Japan, and
especially of Europe and across to New England, it makes its evil
presence felt among the fishermen. Numerous fossil species of _Lamna_
occur, known by the long knife-like flexuous teeth, each having one or
two small cusps at its base.
[Illustration: FIG. 330.--Mackerel-shark, _Isuropsis dekayi_ Gill.
Pensacola, Fla.]
In the closely related genus, _Isurus_, the mackerel-sharks, this cusp
is wanting, while in _Isuropsis_ the dorsal fin is set farther back.
In each of these genera the species reach a length of 20 to 25 feet.
Each is strong, swift, and voracious. _Isurus oxyrhynchus_ occurs
in the Mediterranean, _Isuropsis dekayi_, in the Gulf of Mexico, and
_Isuropsis glauca_, from Hawaii and Japan westward to the Red Sea.
=Man-eating Sharks.=--Equally swift and vastly stronger than these
mackerel-sharks is the man-eater, or great white shark, _Carcharodon
carcharias_. This shark, found occasionally in all warm seas, reaches a
length of over thirty feet and has been known to devour men. According
to Linnæus, it is the animal which swallowed the prophet Jonah. "Jonam
Prophetum," he observes, "ut veteris Herculem trinoctem, in hujus
ventriculo tridui spateo bæsisse, verosimile est."
[Illustration: FIG. 331.--Tooth of _Isurus hastalis_ (Agassiz).
Miocene. Family _Lamnidæ_. (After Nicholson.)]
It is beyond comparison the most voracious of fish-like animals. Near
Soquel, California, the writer obtained a specimen in 1880, with a
young sea-lion (_Zalophus_) in its stomach. It has been taken on the
coasts of Europe, New England, Carolina, California, Hawaii, and Japan,
its distribution evidently girdling the globe. The genus _Carcharodon_
is known at once by its broad, evenly triangular, knife-like teeth,
with finely serrated edges, and without notch or cusp of any kind. But
one species is now living. Fossil teeth are found from the Eocene. One
of these, _Carcharodon megalodon_ (Fig. 332), from fish-guano deposits
in South Carolina and elsewhere, has teeth nearly six inches long. The
animal could not have been less than ninety feet in length. These huge
sharks can be but recently extinct, as their teeth have been dredged
from the sea-bottom by the _Challenger_ in the mid-Pacific.
Fossil teeth of _Lamna_ and _Isurus_ as well as of _Carcharodon_ are
found in great abundance in Cretaceous and Tertiary rocks. Among the
earlier species are forms which connect these genera very closely.
The fossil genus _Otodus_ must belong to the _Lamnidæ_. Its massive
teeth with entire edges and blunt cusps at base are common in
Cretaceous and Tertiary deposits. The teeth are formed much as
in _Lamna_, but are blunter, heavier, and much less effective as
instruments of destruction. The extinct genus _Corax_ is also placed
here by Woodward.
[Illustration: FIG. 332.--_Carcharodon megalodon_ Charlesworth.
Miocene. Family _Lamnidæ_. (After Zittel.)]
=Family Cetorhinidæ, or Basking Sharks.=--The largest of all living
sharks is the great basking shark (_Cetorhinus maximus_), constituting
the family of _Cetorhinidæ_. This is the largest of all fishes,
reaching a length of thirty-six feet and an enormous weight. It is a
dull and sluggish animal of the northern seas, almost as inert as a
sawlog, often floating slowly southward in pairs in the spring and
caught occasionally by whalers for its liver. When caught, its huge
flabby head spreads out wide on the ground, its weight in connection
with the great size of the mouth-cavity rendering it shapeless.
Although so clumsy and without spirit, it is said that a blow with its
tail will crush an ordinary whaleboat. The basking shark is known on
all northern coasts, but has most frequently been taken in the North
Sea, and about Monterey Bay in California. From this locality specimens
have been sent to the chief museums of Europe. In its external
characters the basking shark has much in common with the man-eater.
Its body is, however, relatively clumsy forward; its fins are lower,
and its gill-openings are much broader, almost meeting under the
throat. The great difference lies in the teeth, which in _Cetorhinus_
are very small and weak, about 200 in each row. The basking shark,
also called elephant-shark and bone-shark, does not pursue its prey,
but feeds on small creatures to be taken without effort. Fossil teeth
of _Cetorhinus_ have been found from the Cretaceous, as also fossil
gill-rakers, structures which in this shark are so long as to suggest
whalebone.
[Illustration: FIG. 333.--Basking Shark, _Cetorhinus maximus_ (Gunner).
France.]
=Family Rhineodontidæ.=--The whale-sharks, _Rhineodontidæ_, are
likewise sluggish monsters with feeble teeth and keeled tails. From
_Cetorhinus_ they differ mainly in having the last gill-opening
above the pectorals. There is probably but one species, _Rhineodon
typicus_, of the tropical Pacific, straying northward to Florida, Lower
California, and Japan.
=The Carcharioid Sharks, or Requins.=--The largest family of recent
sharks is that of _Carchariidæ_ (often called _Galeorhinidæ_, or
_Galeidæ_), a modern offshoot from the Lamnoid type, and especially
characterized by the presence of a third eyelid, the nictitating
membrane, which can be drawn across the eye from below. The
heterocercal tail has no keel; the end is bent upward; both dorsal
fins are present, and the first is well in front of the ventral fins;
the last gill-opening over the base of the pectoral, the head normally
formed; these sharks are ovoviviparous, the young being hatched in a
sort of uterus, with or without placental attachment.
Some of these sharks are small, blunt-toothed, and innocuous. Others
reach a very large size and are surpassed in voracity only by the
various _Lamnidæ_.
The genera _Cynias_ and _Mustelus_, comprising the soft-mouthed or
hound-sharks, have the teeth flat and paved, while well-developed
spiracles are present. These small, harmless sharks abound on almost
all coasts in warm regions, and are largely used as food by those
who do not object to the harsh odor of shark's flesh. The best-known
species is _Cynias canis_ of the Atlantic. By a regular gradation of
intermediate forms, through such genera as _Rhinotriacis_ and _Triakis_
with tricuspid teeth, we reach the large sharp-toothed members of
this family. _Galeus_ (or _Galeorhinus_) includes large sharks having
spiracles, no pit at the root of the tail, and with large, coarsely
serrated teeth. One species, the soup-fin shark (_Galeus zyopterus_),
is found on the coast of California, where its fins are highly valued
by the Chinese, selling at from one to two dollars for each set. The
delicate fin-rays are the part used, these dissolving into a finely
flavored gelatine. The liver of this and other species is used in
making a coarse oil, like that taken from the dogfish. Other species
of _Galeus_ are found in other regions, _Galeus galeus_ being known in
England as tope, _Galeus japonicus_ abounding in Japan.
[Illustration: FIG. 334.--Soup-fin Shark, _Galeus zyopterus_ (Jordan &
Gilbert). Monterey.]
_Galeocerdo_ differs mainly in having a pit at the root of the tail.
Its species, large, voracious, and tiger-spotted, are found in warm
seas and known as tiger-sharks (_Galeocerdo maculatus_ in the Atlantic,
_Galeocerdo tigrinus_ in the Pacific).
The species of _Carcharias_ (_Carcharhinus_ of Blainville) lack the
spiracles. These species are very numerous, voracious, armed with sharp
teeth, broad or narrow, and finely serrated on both edges. Some of
these sharks reach a length of thirty feet. They are very destructive
to other fishes, and often to fishery apparatus as well. They are
sometimes sought as food, more often for the oil in their livers, but,
as a rule, they are rarely caught except as a measure for getting
rid of them. Of the many species the best known is the broad-headed
_Carcharias lamia_, or cub-shark, of the Atlantic. This the writer has
taken with a great hook and chain from the wharves at Key West. These
great sharks swim about harbors in the tropics, acting as scavengers
and occasionally seizing arm or leg of those who venture within their
reach. One species (_Carcharias nicaraguensis_) is found in Lake
Nicaragua, the only fresh-water shark known, although some run up the
brackish mouth of the Ganges and into Lake Pontchartrain. _Carcharias
japonicus_ abounds in Japan.
[Illustration: FIG. 335.--Cub-shark, _Carcharias lamia_ Rafinesque.
Florida.]
A closely related genus is _Prionace_, its species _Prionace glauca_,
the great blue shark, being slender and swift, with the dorsal
farther back than in _Carcharias_. Of the remaining genera the most
important is _Scoliodon_, small sharks with oblique teeth which have
no serrature. One of these, _Scoliodon terræ-novæ_, is the common
sharp-nosed shark of our Carolina coast. Fossil teeth representing
nearly all of these genera are common in Tertiary rocks.
Probably allied to the _Carchariidæ_ is the genus _Corax_, containing
large extinct sharks of the Cretaceous with broadtriangular serrate
teeth, very massive in substance, and without denticles. As only the
teeth are known, the actual relations of the several species of _Corax_
are not certainly known, and they may belong to the _Lamnidæ_.
[Illustration: FIG. 336.--Teeth of _Corax pristodontus_.]
=Family Sphyrnidæ, or Hammer-head Sharks.=--The _Sphyrnidæ_, or
hammer-headed sharks, are exactly like the _Carchariidæ_ except that
the sides of the head are produced, so as to give it the shape of a
hammer or of a kidney, the eye being on the produced outer edge. The
species are few, but mostly widely distributed; rather large, voracious
sharks with small sharp teeth.
The true hammer-head, _Sphyrna zygæna_, Fig. 337, is common from the
Mediterranean to Cape Cod, California, Hawaii, and Japan. The singular
form of its head is one of the most extraordinary modifications
shown among fishes. The bonnet-head (_Sphyrna tiburo_) has the head
kidney-shaped or crescent-shaped. It is a smaller fish, but much the
same in distribution and habits. Intermediate forms occur, so that
with all the actual differences we must place the _Sphyrnidæ_ all in
one genus. Fossil hammer-heads occur in the Miocene, but their teeth
are scarcely different from those of _Carcharias_. _Sphyrna prisca_,
described by Agassiz, is the primeval species.
=The Order of Tectospondyli.=--The sharks and rays having no anal
fin and with the calcareous lamellæ arranged in one or more rings
around a central axis constitute a natural group to which, following
Woodward, we may apply the name of _Tectospondyli_. The _Cyclospondyli_
(_Squalidæ_, etc.) with one ring only of calcareous lamellæ may be
included in this order, as also the rays, which have tectospondylous
vertebræ and differ from the sharks as a group only in having the
gill-openings relegated to the lower side by the expansion of the
pectoral fins. The group of rays and Hasse's order of _Cyclospondyli_
we may consider each as a suborder of _Tectospondyli_. The origin of
this group is probably to be found in or near the _Cestraciontes_,
as the strong dorsal spines of the _Squalidæ_ resemble those of the
_Heterodontidæ_.
[Illustration: FIG. 337.--Hammer-head Shark, _Sphyrna zygæna_ L.
Hindustan. (After Day.)]
=Suborder Cyclospondyli.=--In this group the vertebræ have the
calcareous lamellæ arranged in a single ring about the central axis.
The anal fin, as in all the tectospondylous sharks and rays, is
wanting. In all the asterospondylous sharks, as in the _Ichthyotomi_,
_Acanthodei_, and _Chimæras_, this fin is present. It is present in
almost all of the bony fishes. All the species have spiracles, and
in all are two dorsal fins. None have the nictitating membrane, and
in all the eggs are hatched internally. Within the group there is
considerable variety of form and structure. As above stated, we have
a perfect gradation among _Tectospondyli_ from true sharks, with the
gill-openings lateral, to rays, which have the gill-opening on the
ventral side, the great expansion of the pectoral fins, a character of
relatively recent acquisition, having crowded the gill-openings from
their usual position.
=Family Squalidæ.=--The largest and most primitive family of
_Cyclospondyli_ is that of the _Squalidæ_, collectively known as
dogfishes or skittle-dogs. In the _Squalidæ_ each dorsal fin has a
stout spine in front, the caudal is bent upward and not keeled, and the
teeth are small and varied in form, usually not all alike in the same
jaw.
[Illustration: FIG. 338.--Dogfish, _Squalus acanthias_ L. Gloucester,
Mass.]
The genus _Squalus_ includes the dogfishes, small, greedy sharks
abundant in almost all cool seas and in some tropical waters. They
are known by the stout spines in the dorsal fins and by their sharp,
squarish cutting teeth. They are largely sought by fishermen for
the oil in their livers, which is used to adulterate better oils.
Sometimes 20,000 have been taken in one haul of the net. They are very
destructive to herrings and other food-fishes. Usually the fishermen
cut out the liver, throwing the shark overboard to die or to be cast
on the beach. In northern Europe and New England _Squalus acanthias_
is abundant. _Squalus sucklii_ replaces it in the waters about Puget
Sound, and _Squalus mitsukurii_ in Japan and Hawaii. Still others
are found in Chile and Australia. The species of _Squalus_ live near
shore and have the gray color usual among sharks. Allied forms perhaps
hardly different from _Squalus_ are found in the Cretaceous rocks and
have been described as _Centrophoroides_. Other genera related to
_Squalus_ live in greater depths, from 100 to 600 fathoms, and these
are violet-black. Some of the deep-water forms are the smallest of
all sharks, scarcely exceeding a foot in length. _Etmopterus spinax_
lives in the Mediterranean, and teeth of a similar species occur in the
Italian Pliocene rocks. _Etmopterus lucifer_,[150] a deep-water species
of Japan, has a brilliant luminous glandular area along the sides of
the belly. Other small species of deeper waters belong to the genera
_Centrophorus_, _Centroscymnus_, and _Deania_. In some of these species
the scales are highly specialized, pedunculate, or having the form of
serrated leaves. Some species are Arctic, the others are most abundant
about Misaki in Japan and the Madeira Islands, two regions especially
rich in semi-bathybial types. Allied to the _Squalidæ_ is the small
family of _Oxynotidæ_ with short bodies and strong dorsal spine.
_Oxynotus centrina_ is found in the Mediterranean, and its teeth occur
in the Miocene.
[Illustration: FIG. 339.--_Etmopterus lucifer_ Jordan & Snyder. Misaki,
Japan.]
=Family Dalatiidæ.=--The _Dalatiidæ_, or scymnoid sharks, differ from
the _Squalidæ_ almost solely in the absence of dorsal spines. The
smaller species belonging to _Dalatias_ (_Scymnorhinus_, or _Scymnus_),
_Dalatias licha_, etc., are very much like the dogfishes.
They are, however, nowhere very common. The teeth of _Dalatias major_
exist in Miocene rocks. In the genus _Somniosus_ the species are of
very much greater size, _Somniosus microcephalus_ attaining the length
of about twenty-five feet. This species, known as the sleeper-shark or
Greenland shark, lives in all cold seas and is an especial enemy of
the whale, from which it bites large masses of flesh with a ferocity
hardly to be expected from its clumsy appearance. From its habit of
feeding on fish-offal, it is known in New England as "gurry-shark." Its
small quadrate teeth are very much like those of the dogfish, their
tips so turned aside as to form a cutting edge. The species is stout
in form and sluggish in movement. It is taken for its liver in the
north Atlantic on both coasts in Puget Sound and Bering Sea, and I have
seen it in the markets of Tokyo. In Alaska it abounds about the salmon
canneries feeding on the refuse.
=Family Echinorhinidæ.=--The bramble-sharks, _Echinorhinidæ_, differ
in the posterior insertion of the very small dorsal fins, and in the
presence of scattered round tubercles, like the thorns of a bramble
instead of shagreen. The single species, _Echinorhinus spinosus_
reaches a large size. It is rather scarce on the coasts of Europe,
and was once taken on Cape Cod. The teeth of an extinct species,
_Echinorhinus richardi_, are found in the Pliocene.
[Illustration: FIG. 340.--Brain of Monkfish, _Squatina squatina_ L.
(After Duméril.)]
=Suborder Rhinæ.=--The suborder _Rhinæ_ includes those sharks having
the vertebræ tectospondylous, that is, with two or more series of
calcified lamellæ, as on the rays. They are transitional forms, as
near the rays as the sharks, although having the gill-openings rather
lateral than inferior, the great pectoral fins being separated by a
notch from the head.
The principal family is that of the angel-fishes, or monkfishes
(_Squatinidæ_). In this group the body is depressed and flat like that
of a ray. The greatly enlarged pectorals form a sort of shoulder in
front alongside of the gill-openings, which has suggested the bend
of the angel's wing. The dorsals are small and far back, the tail
is slender with small fins, all these being characters shared by the
rays. But one genus is now extant, widely diffused in warm seas. The
species if really distinct are all very close to the European _Squatina
squatina_. This is a moderate-sized shark of sluggish habit feeding on
crabs and shells, which it crushes with its small, pointed, nail-shaped
teeth. Numerous fossil species of _Squatina_ are found from the
Triassic and Cretaceous, _Squatina alifera_ being the best known.
[Illustration: FIG. 341.--Saw-shark, _Pristiophorus japonicus_ Günther.
Specimen from Nagasaki.]
=Family Pristiophoridæ, or Saw-sharks.=--Another highly aberrant family
is that of the sawsharks, _Pristiophoridæ_. These are small sharks,
much like the _Dalatiidæ_ in appearance, but with the snout produced
into a long flat blade, on either side of which is a row of rather
small sharp enameled teeth. These teeth are smaller and sharper than
in the sawfish (_Pristis_), and the whole animal is much smaller than
its analogue among the rays. This saw must be an effective weapon
among the schools of herring and anchovies on which the sawsharks
feed. The true teeth are small, sharp, and close-set. The few species
of sawsharks are marine, inhabiting the shores of eastern Asia and
Australia. _Pristiophorus japonicus_ is found rather sparsely along the
shores of Japan. The vertebræ in this group are also tectospondylous.
Both the _Squatina_ and _Pristiophorus_ represent a perfect transition
from the sharks and rays. We regard them as sharks only because the
gill-openings are on the side, not crowded downward to the under side
of the body-disk. As fossil, _Pristiophorus_ is known only from a few
detached vertebræ found in Germany.
=Suborder Batoidei, or Rays.=--The suborder of _Batoidei_, _Rajæ_,
or _Hypotrema_, including the skates and rays, is a direct modern
offshoot from the ancestors of tectospondylous sharks, its characters
all specialized in the direction of life on the bottom with a food of
shells, crabs, and other creatures less active than fishes.
The single tangible distinctive character of the rays as a whole lies
in the position of the gill-openings, which are directly below the disk
and not on the side of the neck in all the sharks. This difference
in position is produced by the anterior encroachment of the large
pectoral fins, which are more or less attached to the side of the
head. By this arrangement, which aids in giving the body the form of a
flat disk, the gill-openings are limited and forced downward. In the
_Squatinidæ_ (angel-fishes) and the _Pristiophoridæ_ (sawsharks) the
gill-openings have an intermediate position, and these families might
well be referred to the _Batoidei_, with which group they agree in the
tectospondylous vertebræ.
Other characters of the rays, appearing progressively, are the widening
of the disk, through the greater and greater development of the fins,
the reduction of the tail, which in the more specialized forms becomes
a long whip, the reduction, more and more posterior insertion, and the
final loss of the dorsal fins, which are always without spine, the
reduction of the teeth to a tessellated pavement, then finally to flat
plates and the retention of the large spiracle. Through this spiracle
the rays breathe while lying on the bottom, thus avoiding the danger of
introducing sand into their gills, as would be done if they breathed
through the mouth. In common with the cyclospondylous sharks, all the
rays lack the anal fin. The rays rarely descend to great depths in
the sea. The different members have varying relations, but the group
most naturally divides into thick-tailed rays or skates (_Sarcura_)
and whip-tailed rays or sting-rays (_Masticura_). The former are much
nearer to the sharks and also appear earliest in geological times.
=Pristididæ, or Sawfishes.=--The sawfishes, _Pristididæ_, are long,
shark-like rays of large size, having, like the sawsharks, the snout
prolonged into a very long and strong flat blade, with a series of
strong enameled teeth implanted in sockets along either side of it.
These teeth are much larger and much less sharp than in the sawsharks,
but they are certainly homologous with these, and the two groups must
have a common descent, distinct from that of the other rays. Doubtless
when taxonomy is a more refined art they will constitute a small
suborder together. This character of enameled teeth on the snout would
seem of more importance than the position of the gill-openings or
even the flattening and expansion of the body. The true teeth in the
sawfishes are blunt and close-set, pavement-like as befitting a ray.
(See Fig. 152.)
[Illustration: FIG. 342.--Sawfish, _Pristis pectinatus_ Latham.
Pensacola, Fla.]
The sawfishes are found chiefly in river-mouths of tropical America
and West Africa: _Pristis pectinatus_ in the West Indies; _Pristis
zephyreus_ in western Mexico; and _Pristis pectinatus_ in the Senegal.
They reach a length of ten to twenty feet, and with their saws they
make great havoc among the schools of mullets and sardines on which
they feed. The stories of their attacks on the whale are without
foundation. The writer has never found any of the species in the
open sea. They live chiefly in the brackish water of estuaries and
river-mouths.
Fossil teeth of sawfishes occur in abundance in the Eocene. Still
older are vertebræ from the Upper Cretaceous at Maestricht. In
_Propristis schweinfurthi_ the tooth-sockets are not yet calcified.
In _Sclerorhynchus atavus_, from the Upper Cretaceous, the teeth
are complex in form, with a "crimped" or stellate base and a sharp,
backward-directed enameled crown.
=Rhinobatidæ, or Guitar-fishes.=--The _Rhinobatidæ_ (guitar-fishes)
are long-bodied, shovel-nosed rays, with strong tails; they are
ovoviviparous, hatching the eggs within the body. The body, like that
of the shark or sawfish, is covered with nearly uniform shagreen.
The numerous species abound in all warm seas; they are olive-gray
in color and feed on small animals of the seabottoms. The length
of the snout differs considerably in different species, but in all
the body is relatively long and strong. Most of the species belong
to _Rhinobatus_. The best-known American species are _Rhinobatus
lentiginosus_ of Florida and _Rhinobatus productus_ of California.
The names guitar-fish, fiddler-fish, etc., refer to the form of the
body. Numerous fossil species, allied to the recent forms, occur from
the Jurassic. Species much like _Rhinobatus_ occur in the Cretaceous
and Eocene. _Tamiobatis vetustus_, lately described by Dr. Eastman
from a skull found in the Devonian of eastern Kentucky, the oldest
ray-like fish yet known, is doubtless the type of a distinct family,
_Tamiobatidæ_. It is more likely a shark however than a ray, although
the skull has a flattened ray-like form.
[Illustration: FIG. 343.--Guitar-fish, _Rhinobatus lentiginosus_
Garman. Charleston, S. C.]
Closely related to the _Rhinobatidæ_ are the _Rhinidæ_
(_Rhamphobatidæ_), a small family of large rays shaped like the
guitar-fishes and found on the coast of Asia. _Rhina ancylostoma_
extends northward to Japan.
In the extinct family of _Astrodermidæ_, allied to the _Rhinobatidæ_,
the tail has two smooth spines and the skin is covered with tubercles.
In _Belemnobatis sismondæ_ the tubercles are conical; in _Astrodermus
platypterus_ they are stellate.
=Rajidæ, or Skates.=--The _Rajidæ_, skates, or rays, inhabit the colder
waters of the globe and are represented by a large number of living
species. In this family the tail is stout, with two-rayed dorsal fins
and sometimes a caudal fin. The skin is variously armed with spines,
there being always in the male two series of specialized spinous hooks
on the outer edge of the pectoral fin. There is no serrated spine or
"sting," and in all the species the eggs are laid in leathery cases,
which are "wheelbarrow-shaped," with a projecting tube at each of
the four angles. The size of this egg-case depends on the size of the
species, ranging from three to about eight inches in length. In some
species more than one egg is included in the same case.
Most of the species belong to the typical genus _Raja_, and these are
especially numerous on the coasts of all northern regions, where they
are largely used as food. The flesh, although rather coarse and not
well flavored, can be improved by hot butter, and as "raie au beurre
noir" is appreciated by the epicure. The rays of all have small rounded
teeth, set in a close pavement.
[Illustration: FIG. 344.--Common Skate, _Raja erinacea_ Mitchill. Woods
Hole, Mass.]
Some of the species, known on our coasts as "barn-door skates," reach
a length of four or five feet. Among these are _Raja lævis_ and _Raja
ocellata_ on our Atlantic coast, _Raja binoculata_ in California,
and _Raja tengu_ in Japan. The small tobacco-box skate, brown with
black spots, abundant on the New England coast, is _Raja erinacea_.
The corresponding species in California is _Raja inornata_, and in
Japan _Raja kenojei_. Numerous other species, _Raja batis_, _clavata_,
_circularis_, _fullonica_, etc., occur on the coasts of Europe. Some
species are variegated in color, with eye-like spots or jet-black
marblings. Still others, living in deep waters, are jet-black with
the body very soft and limp. For these Garman has proposed the
generic name _Malacorhinus_, a name which may come into general use
when the species are better known. In the deep seas rays are found
even under the equator. In the south-temperate zone the species are
mostly generically distinct, _Psammobatis_ being a typical form,
differing from _Raja_. _Discobatus sinensis_, common in China and
Japan, is a shagreen-covered form, looking like a _Rhinobatus_. It
is, however, a true ray, laying its eggs in egg-cases, and with the
pectorals extending on the snout. Fossil _Rajidæ_, known by the teeth
and bony tubercles, are found from the Cretaceous onward. They belong
to _Raja_ and to the extinct genera _Dynatobatis_, _Oncobatis_, and
_Acanthobatis_. The genus _Arthropterus_ (_rileyi_) from the Lias,
known from a large pectoral fin, with distinct cylindrical-jointed
rays, may have been one of the _Rajidæ_, or perhaps the type of a
distinct family, _Arthropteridæ_.
[Illustration: FIG. 345.--Numbfish, _Narcine brasiliensis_ Henle,
showing electric cells. Pensacola, Fla.]
=Narcobatidæ, or Torpedoes.=--The torpedoes, or electric rays
(_Narcobatidæ_), are characterized by the soft, perfectly smooth skin,
by the stout tail with rayed fins, and by the ovoviviparous habit,
the eggs being hatched internally. In all the species is developed
an elaborate electric organ, muscular in its origin and composed of
many hexagonal cells, each filled with soft fluid. These cells are
arranged under the skin about the back of the head and at the base of
the pectoral fin, and are capable of benumbing an enemy by means of a
severe electric shock. The exercise of this power soon exhausts the
animal, and a certain amount of rest is essential to recovery.
The torpedoes, also known as crampfishes or numbfishes, are peculiarly
soft to the touch and rather limp, the substance consisting largely of
watery or fatty tissues. They are found in all warm seas. They are not
often abundant, and as food they have not much value.
Perhaps the largest species is _Tetronarce occidentalis_, the crampfish
of our Atlantic coast, black in color, and said sometimes to weigh 200
pounds. In California _Tetronarce californica_ reaches a length of
three feet and is very rarely taken, in warm sandy bays. _Tetronarce
nobiliana_ in Europe is much like these two American species. In the
European species, _Narcobatus torpedo_, the spiracles are fringed
and the animal is of smaller size. To _Narcine_ belong the smaller
numbfish, or "entemedor," of tropical America. These have the spiracles
close behind the eyes, not at a distance as in _Narcobatus_ and
_Tetronarce_. _Narcine brasiliensis_ is found throughout the West
Indies, and _Narcine entemedor_ in the Gulf of California. _Astrape_,
a genus with but one dorsal fin, is common in southern Japan. Fossil
_Narcobatus_ and _Astrape_ occur in the Eocene, one specimen of the
former nearly five feet long. Vertebræ of _Astrape_ occur in Prussia in
the amber-beds.
[Illustration: FIG. 346.--Teeth of _Janassa linguæformis_ Atthey.
Carboniferous. Family _Petalodontidæ_. (After Nicholson.)]
=Petalodontidæ.=--Near the _Squatinidæ_, between the sharks and the
rays, Woodward places the large extinct family of _Petalodontidæ_, with
coarsely paved teeth each of which is elongate with a central ridge and
one or more strong roots at base. The best-known genera are _Janassa_
and _Petalodus_, widely distributed in Carboniferous time. _Janassa_ is
a broad flat shark, or, perhaps, a skate, covered with smooth shagreen.
The large pectoral fins are grown to the head; the rather large ventral
fins are separated from them. The tail is small, and the fins, as in
the rays, are without spines. The teeth bear some resemblance to those
of _Myliobatis_. _Janassa_ is found in the coal-measures of Europe
and America, and other genera extend upward from the Subcarboniferous
limestones, disappearing near the end of Carboniferous time.
_Petalodus_ is equally common, but known only from the teeth. Other
widely distributed genera are _Ctenoptychius_ and _Polyrhizodus_.
[Illustration: FIG. 347.--_Polyrhizodus radicans_ Agassiz. Family
_Petalodontidæ_. Carboniferous of Ireland. (After McCoy.)]
These forms may be intermediate between the skates and the sting-rays.
In dentition they resemble most the latter.
Similar to these is the extinct family of _Pristodontidæ_ with one
large tooth in each jaw, the one hollowed out to meet the other. It is
supposed that but two teeth existed in life, but that is not certain.
Nothing is known of the rest of the body in _Pristodus_, the only genus
of the group.
=Dasyatidæ, or Sting-rays.=--In the section _Masticura_ the tail is
slender, mostly whip-like, without rayed dorsal or caudal fins, and
it is usually armed with a very long spine with saw-teeth projecting
backward. In the typical forms this is a very effective weapon, being
wielded with great force and making a jagged wound which in man rarely
heals without danger of blood-poisoning. There is no specific poison,
but the slime and the loose cuticle of the spine serve to aggravate
the irregular cut. I have seen one sting-ray thrust this spine through
the body of another lying near it in a boat. Occasionally two or
three of these spines are present. In the more specialized forms of
sting-rays this spine loses its importance. It becomes very small and
not functional, and is then occasionally or even generally absent in
individuals.
The common sting-rays, those in which the caudal spine is most
developed, belong to the family of _Dasyatidæ_. This group is
characterized by the small skate-like teeth and by the non-extension
of the pectoral rays on the head. The skin is smooth or more or less
rough. These animals lie flat on the sandy bottoms in nearly all seas,
feeding on crabs and shellfish. All hatch the eggs within the body.
The genus _Urolophus_ has a rounded disk, and a stout, short tail
with a caudal fin. It has a strong spine, and for its size is the
most dangerous of the sting-rays. _Urolophus halleri_, the California
species, was named for a young man who was stung by the species at
the time of its first discovery at San Diego in 1863. _Urolophus
jamaicensis_ abounds in the West Indies, _Urolophus mundus_ at Panama,
and _Urolophus fuscus_ in Japan. None of the species reach Europe. The
true sting-ray (stingaree, or clam-cracker), _Dasyatis_, is more widely
diffused and the species are very closely related. In these species
the body is angular and the tail whip-like. Some of the species reach
a length of ten or twelve feet. None have any economic value, and all
are disliked by fishermen. _Dasyatis pastinaca_ is common in Europe,
_Dasyatis centrura_ along our Atlantic coast, _Dasyatis sabina_ ascends
the rivers of Florida, and _Dasyatis dipterura_ abounds in the bay of
San Diego. Other species are found in tropical America, while still
others (_Dasyatis akajei_, _kuhlii_, _zugei_, etc.) swarm in Japan and
across India to Zanzibar.
[Illustration: FIG. 348.--Sting-ray, _Dasyatis sabina_ Le Sueur.
Galveston.]
_Pteroplatea_, the butterfly-ray, has the disk very much broader than
long, and the trivial tail is very short, its little spine more often
lost than present. Different species of this genus circle the globe:
_Pteroplatea maclura_, on our Atlantic coast; _Pteroplatea marmorata_,
in California; _Pteroplatea japonica_, in Japan; and _Pteroplatea
altavela_, in Europe. They are all very much alike, olive, with the
brown upper surface pleasingly mottled and spotted.
Sting-rays of various types, _Tæniura_, _Urolophus_, etc., occur as
fossils from the Eocene onward. A complete skeleton called _Xiphotrygon
acutidens_, distinguished from _Dasyatis_ by its sharp teeth, is
described by Cope from the Eocene of Twin Creek in Wyoming. Vertebræ of
_Urolophus_ are found in German Eocene. _Cyclobatis_ (_oligodactylus_),
allied to _Urolophus_, with a few long pectoral rays greatly produced,
extending over the tail and forming a rayed wreath-like projection over
the snout, is known from the Lower Cretaceous.
=Myliobatidæ.=--The eagle-rays, _Myliobatidæ_, have the pectoral fins
extended to the snout, where they form a sort of rayed pad. The teeth
are very large, flat, and laid in mosaic. The whip-like tail is much
like that in the _Dasyatidæ_, but the spine is usually smaller. The
eagle-like appearance is suggested by the form of the skull. The eyes
are on the side of the head with heavy eyebrows above them. The species
are destructive to clams and oysters, crushing them with their strong
flat teeth.
In _Aëtobatus_ the teeth are very large, forming but one row. The
species _Aëtobatus narinari_ is showily colored, brown with yellow
spots, the body very angular, with long whip-like tail. It is found
from Brazil to Hawaii and is rather common.
In _Myliobatis_ the teeth are in several series. The species are many,
and found in all warm seas. _Myliobatis aquila_ is the eagle-ray of
Europe, _Myliobatis californicus_ is the batfish of California, and
_Myliobatis tobijei_ takes its place in Japan.
In _Rhinoptera_ the snout is notched and cross-notched in front so that
it appears as if ending in four lobes at the tip. These "cow-nosed
rays," or "whipparees," root up the soft bottoms of shallow bays in
their search for clams, much as a drove of hogs would do it. The common
American species is _Rhinopterus bonasus_. _Rhinoptera steindachneri_
lives in the Gulf of California.
Teeth and spines of all these genera are common as fossils from the
Eocene onwards, as well as many of the extinct genus, _Ptychodus_,
with cyclospondylous vertebræ. _Ptychodus mammilaris_, _rugosus_,
and _decurrens_ are characteristic of the Cretaceous of England.
_Myliobatis dixoni_ is common in the European Eocene, as is also
_Myliobatis toliapicus_ and _Aëtobatis irregularis_. _Apocopodon
seriacus_ is known from the Cretaceous of Brazil.
[Illustration: FIG. 349.--Eagle-ray, _Aëtobatis narinari_ (Euphrasen).
Cedar Keys, Fla.]
=Family Psammodontidæ.=--The _Psammodontidæ_ are known only from the
teeth, large, flat, or rounded and finely dotted or roughened on the
upper surface, as the name _Psammodus_ (~psammos~, sand; ~odous~,
tooth) would indicate. The way in which the jaws lie indicates that
these teeth belonged to rays rather than sharks. Numerous species
have been described, mostly from the Subcarboniferous limestones.
_Archæobatis gigas_, perhaps, as its name would indicate, the primeval
skate, is from the Subcarboniferous limestone of Greencastle, Indiana.
Teeth of numerous species of _Psammodus_ and _Copodus_ are found
in many rocks of Carboniferous age. _Psammodus rugosus_ common in
Carboniferous rocks of Europe.
[Illustration: FIG. 350.--Devil-ray or Sea-devil, _Manta birostris_
(Walbaum). Florida.]
=Family Mobulidæ.=--The sea-devils, _Mobulidæ_, are the mightiest of
all the rays, characterized by the development of the anterior lobe
of the pectorals as a pair of cephalic fins. These stand up like
horns or cars on the upper part of the head. The teeth are small and
flat, tubercular, and the whip-like tail is with or without spine.
The species are few, little known, and inordinately large, reaching a
width of more than twenty feet and a weight, according to Risso, of
1250 pounds. When harpooned it is said that they will drag a large boat
with great swiftness. The manta, or sea-devil, of tropical America is
_Manta birostris_. It is said to be much dreaded by the pearl-fishers,
who fear that it will devour them "after enveloping them in its vast
wings." It is not likely, however, that the manta devours anything
larger than the pearl-oyster itself. _Manta hamiltoni_ is a name given
to a sea-devil of the Gulf of California. The European species _Mobula
edentula_ reaches a similarly enormous size, and _Mobula hypostoma_
has been scantily described from Jamaica and Brazil. _Mobula japonica_
occurs in Japan. A foetus in my possession from a huge specimen taken
at Misaki is nearly a foot across. In _Mobula_ (_Cephaloptera_) there
are teeth in both jaws, in _Manta_ (_Ceratoptera_) in the lower jaw
only. In _Ceratobatis_ from Jamaica (_C. robertsi_) there are teeth in
the upper jaw only. Otherwise the species of the three genera are much
alike, and from their huge size are little known and rarely seen in
collections. Of _Mobulidæ_ no extinct species are known.
FOOTNOTES:
[150] Dr. Peter Schmidt has made a sketch of this little shark at night
from a living example, using its own light.