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as broken limbs or ribs." It is a somewhat remarkable fact that in places like
Aden, where sharks of various kinds abound, the natives will swim and dive
fearlessly in the open sea, where a European would be almost instantly devoured
by these monsters. The blue shark has the whole of the upper-parts slaty blue,
and the under surface white.



5 24 SHARKS AND XAYS.

Our next representative of the family is the small shark
commonly known as the tope (Galeus canis), which belongs to a
genus including only two species and characterised as follows. The muzzle is
short and the mouth crescent-shaped ; very small spiracles are present ; there is no
pit at the root of the caudal tin, which has only a single notch ; and the teeth,
which are similar in the two jaws, have serrated edges, and a notch on the hinder
border. The common tope, which is usually about 6 feet in length, although it
may grow to 7 feet, is a very widely spread species, ranging over all temperate
and tropical seas, and visiting the shores of such widely separated localities as
California, the British Islands, and Australia. In colour it is dark grey above,
and dirty white beneath. The second living species inhabits the Japanese seas;
and teeth from the Tertiary formations of Europe have been referred to the
genus. In habits the tope is a bottom-haunting species especially during the
winter months and devours other fish, crustaceans, and star-fishes. It is not
unfrequently taken by the line, arid is thus a great source of annoyance to fisher-
men, especially on the Norfolk coast, where considerable numbers are sometimes
hooked. The young are produced alive, and it is stated that there have been
instances of as many as fifty individuals in a single brood.

Having teeth very similar to the true sharks, the five species
known as hammerheads, or hammer-headed sharks, one of which
(Sphyrna malleus) is represented in the illustration on p. 521, form a genus unique
among fishes in the extraordinary conformation of the head. Instead of retain ing
the usual more or less pointed form, the front part of the head of these sharks
is broad, flattened, and expanded on each side into a process, on the flat terminal
surface of which is situated the eye. This, of course, is quite sufficient to dis-
tinguish the genus ; but it may be added that the caudal fin has a single notch
and a pit at its root, there are no spiracles, the nostrils are situated on the
front edge of the head, and the mouth is crescent-shaped. The teeth differ from
those of the true sharks in being similar in both jaws ; their margins being either
smooth or serrated. Hammerheads range over all the warmer seas, the common
species being sometimes taken on the British coast ; and an extinct form occurs
in strata of Miocene age. Growing to a length of some 14 or 15 feet, the common
hammerhead is one of the most formidable and voracious of its tribe, and is much
feared in the Indian seas.

By this somewhat inappropriate title are designated two small
Hounds. . .

British sharks, one of which (Mustelus Icevis) is shown in the lower

figure of the accompanying illustration. Externally these sharks are not unlike
the tope, but the snout is less pointed. As a genus they are characterised by the
rather short muzzle ; the crescent-shaped mouth ; the presence of minute spiracles ;
the absence of a pit at the base of the caudal fin, which has scarcely any lower
lobe; and the slight difference in the size of the two dorsal tins. The teeth,
moreover, are small and numerous, being either blunt or with indistinct cusps.
and forming a kind of pavement-like structure; those in the upper jaw being
similar to those in the lower. The smooth hound, which is the species here
figured, is generally about 4 feet in length, although it may reach to (> feet. The
sides of the back are marked by a series of whitish spots, more distinct in



PORBEAGLE GROUP.



525



the young than in the adult. Feeding on molluscs and crustaceans, this species
(which ranges over most warm seas) produces about a dozen young at a birth,
these being attached by a placental structure to the walls of the uterus of the
parent. Curiously enough such connection is, however, totally wanting in the
young of the other British species ( M. vulgaris). In habits the hounds are bottom-
liaunting species, as indeed might be inferred from the nature of their food. On




SPINY DOG-FISH AND SMOOTH HOUND (1 nat. size).

the English coast the smooth hound generally makes its appearance during the
summer in pursuit of the shoals of pilchard and herring. Several other genera of
this family must be passed over without notice.

THE PORBEAGLE GROUP, Family LAMNIDJE.

Agreeing with the typical sharks in the position of the two spineless dorsal
fins, the members of the present family may be distinguished by the absence of a



5 2 6 SHARKS AND RAYS.

nictitating membrane to the eye; and also by the solid structure of the fully
formed teeth, which are pointed, and in most of the genera relatively large. In
addition to these features, it may be noted that the gill-openings are generally
wide, and the spiracles either minute or wanting. This family dates from the
period of the Chalk, where there occur remains of species some of which are
referable to genera still existing, such as the porbeagles, while others indicate
extinct generic type. The fox-sharks and the gigantic Carcharodon are, however,
unknown before the Tertiary period.

The shark (Lamna cornubica) commonly known to the British

fishermen as the porbeagle a word supposed to be derived from
its porpoise-like appearance and active predatory habits is the type of a genus
containing three existing species, and characterised by the small size of the second
dorsal and anal fin, and the presence of a pit at the root of the caudal fin of which
the lower lobe is much developed and also of a keel along the sides of the tail.
The teeth are narrow and slender, with one or two pairs of small accessory cones
at their bases ; the edges of the main cone being smooth. The common porbeagle
wanders all over the North Atlantic, and has also been taken in Japan; it docs
not commonly exceed 10 feet in length, and its colour is dull grey above and
whitish beneath. Its food chiefly consists of fishes, which are apparently
swallowed whole ; the lancet-like teeth of this shark being apparently more
adapted for seizing and holding than for tearing prey. The porbeagle is stated to
be a viviparous species.

Rondeieti's The most formidable of all the existing members of the group is

Shark. the gigantic Rondeieti's shark (Carcharodon rondeletii), distinguished
from the porbeagles by the great size of the broadly triangular teeth, which have
strongly serrated edges, and may possess basal cusps. The existing species, which
is a purely pelagic creature ranging over all the warmer seas, is known to attain
a length of 40 feet, one of the teeth of a specimen of 36 feet in length measuring
2 inches along the edge of the crown, and If inches across the base. Similar
teeth are found in the Crag deposits of Suffolk, and are referred to the existing
species; but from these same beds, and also from the bottom of the Pacific,
between Polynesia and Australia, there are obtained other teeth of much larger
dimensions, some of them measuring upwards of 5 inches along the edge and
4 inches in basal depth. These teeth evidently indicate sharks beside which the
existing form is a comparative dwarf ; and it is not a little remarkable that the
specimens dredged from the bed of the Pacific indicate that these giants must in
all probability have survived to a comparatively recent date. Observations are,
still required as to the mode of life and breeding-habits of Rondeieti's shark.
Two other species of large sharks constitute the genus Odontaspis. With teeth
almost indistinguishable from those of the porbeagles, these species differ by the
second dorsal and anal fins being nearly as large as the first dorsal, and the
absence of a pit at the root of the caudal fin, and of a keel on the sides of the tail.
Another species not uncommonly met with in British waters is

the fox-shark or thresher (Alopecias vul /><*}, the sole representative
of its genus, and easily recognised by the inordinate length of the upper lobe of
its tail-fin, from which it derives its name. Growing to a length of 15 feet, of



^ASKING-SHARKS. 5 2 7

which more than half is taken up by the tail, this shark has the second dorsal and
anal tins very small ; the caudal tin extremely elongated, and without a pit at its
root; no keel on the sides of the tail; and the teeth, which are similar in both
jaws, of small size, compressed and triangular, with smooth edges.' Like most
sharks, the thresher has a wide range, being abundant throughout the Atlantic and
Mediterranean, and also found off the coasts of New Zealand and California. The
comparatively small size of its teeth indicates that it is not adapted for killing
large prey ; and, as a matter of fact, this shark chiefly feeds upon the various
species of the herring tribe and mackerel, among which it inflicts terrible destruc-
tion. It derives its name of thresher from its habit of beating the water with its
long tail in order to drive the members of the shoals on which it preys into a
compact mass, when they can be the more readily seized ; and its voracity may bo
inferred from the fact of no less than nineteen mackerel and two herrings having
been taken from the stomach of a single individual. It is commonly reported by
sailors that threshers, in company with killers and sword-fish, make attacks on whales
by leaping high in the air and belabouring the unfortunate cetaceans with powerful
blows of their tails as they descend ; but these statements have been generally
discredited by naturalists, apparently on the ground that the teeth of these sharks
arc not adapted for rending the flesh of large animals. It is, however, somewhat
difficult on such grounds to refuse to believe the circumstantial accounts we
possess, and it may be that the threshers join in the fray in order to feed on the
smaller fragments left by their more powerfully armed coadjutors.

The largest of the North Atlantic members of the suborder is

Kn.sk utT-SiicLrk

the basking-shark (Cetorhinus maximus), which now alone represents
a genus with the second dorsal and anal fins very small, a pit at the root of the
caudal fin, a keel on each side of the tail, the gill-clefts very large and wide,
and the teeth very small, numerous, and conical, without basal cusps, and seldom
serrated at the edges. This shark, which grows to a length of over 30 feet, is
regularly hunted on the w r est coast of Iceland for the sake of the oil from its liver,
of which a single fish may yield considerably more than a ton. It derives its
name from its habit of lying motionless during calm, warm weather on the surface
of the water, with the tall first dorsal fin and a considerable portion of its back
exposed ; several individuals often consorting together. The gill-arches are provided
with very long rakers bearing granular tooth-like structures ; and in the young
the muzzle is relatively longer and more pointed than in the adult. Unless
attacked, when it can inflict x blows with its tail capable of staving in the sides of
a boat, this shark is perfectly harmless, its food consisting entirely of small fishes
which swim in shoals, and various invertebrates. Remains of an extinct species
occur in the Pliocene deposits of Belgium, w r hile others from older Tertiary beds
have been tentatively assigned to the genus.

INDO-PACIFIC BASKING-SHARK, Family RHINODONTID^:.

Although resembling the true basking-shark in the large size of its gill-clefts
and the structure of its gill-rakers, the gigantic species (Rhinodon typicus) figured
in the illustration on p. 528 differs in having the mouth and nostrils situated



5 28



SHARKS AND RAYS.



near the extremity of the muzzle, as well as in the backward position of the small
first dorsal fin, which does not reach to the level of the highest point of the back,
instead of standing immediately above it. Moreover, instead of being subcylindrical,
the whole body of this shark is markedly depressed and the huge mouth forms a
nearly oblong aperture, and is armed with bands of very small and numerous
teeth. The sides of the tail bear a well-defined keel, and the lower lobe of the
caudal fin is well developed. In its varied coloration this fish differs markedly
from the majority of sharks, being ornamented with buff spots and stripes upon a
dark ground. Although probably widely distributed within the tropics, this




INDO-PACIFIC BASKING-SHARK (^ nat. Size).






monster has hitherto been met with but locally. For many years the sole evidence
of its existence rested upon a specimen, 15 feet long, brought ashore in Table Bay
in April 1828, which fell into the hands of the late Sir Andrew Smith, who
described and figured it. This specimen was preserved by a French taxidermist,
who sold it to the Paris Museum, where it still remains. Forty years later, in
1868, Dr. Perceval Wright, whilst staying at the Seychelles, met with this shark,
and obtained the first authentic information about it. It does not seem to l>e nuv
in that archipelago, but is very seldom obtained on account of its large size and the
litlieulties attending its capture. Dr. Wright saw specimens which exceed' -d
50 feet in length, and one that was actually measured proved to be more than
45 feet long. Nothing more was heard of the species until Januar}* 1878, in



DOG-FISHES.



5-9



which year the capture of another specimen was reported from the Peruvian coast
near Callao; finally, in the "nineties" it was discovered on the west coast of
Ceylon, where two or three specimens were obtained. One of these was presented
to the British Museum : and, having been mounted, is now exhibited in the Fish
Gallery, where it forms one of the most striking objects, although only a young
example, measuring 17 feet from the end of the snout to the extremity of the tail.
It has been stated that this fish feeds on seaweeds, but it is more probable that
its food is similar to that of the baskinxj-shark.




LESSER SPOTTED DOG-FISH AND ITS EGGS (\ nat. size).

THE DOG-FISHES AND THEIR ALLIES, Family SCYLLHD^J.

Agreeing with the preceding families in the absence of spines to the dorsal fin,
the dog-fishes and their allies may be distinguished from the sharks hitherto
noticed, in which the mouth is inferior in position, by the more backward situation
of the first dorsal, which is placed above or behind the line of the pelvic fins.
They have no nictitating membrane to the eye; and the teeth are small, with
several series generally in use at the same time. In all there are distinct spiracles.

VOL. v. 34



53 o SHARKS AND RAYS.

Represented in British waters by the larger (Scylliuin canicula),
' S and lesser spotted dog-fish (S. catulus), this genus is characterised by
the first dorsal tin being above or behind the line of the pelvic pair; by the origin
of the anal being in advance of the line of that of the second dorsal ; the absence
of serration of the upper edge of the caudal fin; and the small and delicate teeth,
which are arranged in numerous series, and generally have a long central cusp,
flanked l\- one or two small ones on each side. About half a score of species have
been described, ranging over the coast-regions of most temperate and tropical species,
and all of comparatively small size ; the majority having prettily spotted skins.
Their food consists mainly of crustaceans and molluscs ; and their flesh is eaten
not unfrequently by fishermen, while in the Orkneys, where the British species are
more abundant than elsewhere, it is regularly dried for winter consumption. The
shagreen of their skins is also employed in wood-polishing. These sharks lay eggs
of the form shown in our illustration. Fossil dog-fishes date from the period of
the Chalk ; and they are represented in the Kimeridge Clay by the extinct
Palceoscyllium, in which the origin of the second dorsal fin is placed in advance of
that of the small anal.

Among several allied genera we may especially notice the zebra-
other Genera,

shark (Steyostoma tigrinum) of the Indian Ocean, attaining a length

of from 10 to 15 feet, and noticeable for its handsome coloration, which consists of
a brownish yellow ground-colour, marked with black or brown transverse bars
or round spots. In this fish the first dorsal fin is above the line of the pelvic pair,
while the second is in advance of the line of the anal, which is approximated to
the caudal ; the latter being greatly elongated, and equal to half the total length.
Young specimens of this shark are generally met with near the coast, but the
adults are more or less pelagic. Dog-fishes of smaller size from the Indian Ocean
constitute the genus Cfiiloscyllium, in which the first dorsal fin is either above or
behind the line of the pelvics ; while the anal is far behind that of the second
dorsal, and close to the caudal ; the teeth being small and triangular, with or
without lateral cusps. The existing species are very handsomely ornamented with
dark bands and spots. In a fossil state the genus has been recorded from the
Miocene Tertiary. Three bottom-haunting sharks from the Japanese and Australian
seas have been described under the name of Crossorhinus, and are remarkable for
the presence of leaf-like expansions of the skin on the sides of the head. As in
the case of other fish similarly adorned, these structures are probably for the
purpose of attracting prey ; and in order that they may be well concealed, these
sharks have a coloration closely assimilating to that of a rock covered with sea-
weed or corallines.

THE PAVEMENT-TOOTHED SHARKS, Family CESTRACIONTID^:.

The well-known Port Jackson shark (Cestracion pliilipp^) and three allied
species are the sole existing representatives of a family which was exceedingly
abundant during the Secondary epoch. They differ from all the foregoing in
the presence of a strong spine on the front edge of each of the two dorsal fins.
The first dorsal fin is situated above the space between the pectoral and pelvic



PA VEMENT- TO O THED SHARKS.



531



pairs ; and the teeth, of which .several series are in use at the same time, are more
or less blunt and broad, more especially in the hinder part of the jaws, although
those in each oblique row are never fused together into continuous plates. In




PORT JACKSON SHARK (J liat. size).



the existing genus there is no nictitating membrane to the eye; the body is
moderately elongated, with the second dorsal fin in advance of the line of the
anal ; and the mouth is almost or quite terminal. In the dentition, the front teeth
are small, numerous, and
sharp, while the hinder ones
are broad and flattened, with a
slight longitudinal ridge and a
net-like ornamentation. The
spines of the dorsal fins are
smooth, covered on the sides
with a thick layer of ganoin ;
the shagreen is fine ; and the
head is devoid of spines. In
the existing species the egg-
capsules assume a remarkable
screw-like form, quite unlike
that of any other member of
the family. The living mem-
bers of the genus, none of
which exceed 5 feet in length,
have been recorded from the
seas of Japan, Amboyna,
Australia, the Galapagos

Islands, and California ; while remains of extinct forms occur in the Cretaceous
and Upper Jurassic strata of Europe. Very little appears to be known as to their
habits ; but their food is stated to consist principally of molluscs, the hard shells
of which are crushed by the pavement-like hinder teeth.




LOWER JAW OF TORT JACKSON SHARK (J nat. Size).



53 2 SHARKS AND RAYS.

Of the numerous fossil genera of the family only a very brief
>e8 ' mention can be made. One of the earliest is the Carboniferous
Orodus, with teeth very like those of the later Hybodus, ranging from the Trias
to the lower Cretaceous. In the last-named genus the notochord is persistent, the
bluntly conical or cusped teeth have a central and two or more lateral cusps, the
fin-spines are ridged, and there are two hook-like spines In-low each eye. Acrodus,
with a nearly similar range, has, on the other hand, blunt teeth ; while the Jurassic
Asteracantkus differs from Hybodua by its rhomboidal, roughened, and flattened
teeth, and the star-like ornamentation of the spines of the dorsal fins. In
Synechodus of the Chalk all the teeth are cusped ; the anterior ones having a tall
central cusp, flanked with from three to five small lateral pairs. An allied extinct
family (Cochliodontidce), confined to the Carboniferous rocks, differs by the
component teeth of at least one of the oblique rows being fused into a continuous
curved plate, which may be either smooth or ridged. Many of the extinct
representatives of these families exceeded the Port Jackson shark in size.

THE COMB-TOOTHED SHARKS, Family NOTIDANID^R.

A very remarkable family is now represented by the four species of comb-
toothed sharks (Notidanus) and the frill-gilled shark (Cklamydoselache anguineus),
the latter of which is shown in the illustration. Whereas in all other sharks the
gill-clefts are four in number, in the present family they are increased to five or six ;

while there is a further
peculiarity in regard to the
structure of the skull. It has
been already stated (p. 520)
that in the more typical

LOWER TEETH OP EXTINCT COMB-TOOTHED SHARKS. sharks tllC lUnctlOlial lower

jaw is articulated to the

cranium by the intervention of the hyomandibular element; but in the Port
Jackson shark this element becomes reduced in size, and the palatopterygoid bar
(the functional upper jaw) has a facet by which it articulates directly with the
cranium. In the present family, on the other hand, the hyomandibular takes no
share in the suspension of the jaws, which are articulated to the cranium solely
by means of the facet on the palatopterygoid bar ; the latter joining a corre-
sponding facet on the cranium behind the socket for the eye. In addition to their
more numerous gill-slits, the comb -toothed sharks are distinguished external ly
from all those hitherto considered by having only a single dorsal fin, which is
situated far back on the body and has no spine. The eye is devoid of a nictitating
membrane ; the spiracles are small ; and the teeth, of which several series are in
use at the same time, have sharply-pointed cusps.

In the typical genus the body is moderately elongated, the
Typical Genus.

mouth inferior in position, and the gill-openings, which may be either

six or seven in number, are devoid of flaps. The principal teeth consist of a series
of cusps placed upon a long base, all inclining in one direction, and decreasing in
si/.e from the front to the back; the number of these cusps being greater in the




FRILL-GILLED SHARK.



533



teeth of the lower than in those of the upper jaw. With the occasional exception
of some portions of the tail, the notochord persists throughout life. At the present
day the range of the existing members of the genus includes most temperate and
tropical seas, some of the species reaching as much as 15 feet in length. Whereas
in the grey comb-toothed shark (Notidanus griseus), of the Atlantic and Mediter-
ranean, the number of gill-clefts is six, in each of the other three species it is seven.
Fossil species occur from the Pliocene to the middle Jurassic ; many of these, like
the one of which two teeth are shown in the illustration, being of much larger
dimensions than any of the existing forms. As to the habits of these sharks, there
appears to be practically no information.

Friii-GiUed From the typical genus of the family the Japanese frill-gilled

Shark. shark differs by the greatly elongated and slender form of the body ;

and by each of the six gill-clefts being protected by a frill-like flap of skin. The




FRILL-GILLED SHARK.



teeth are also of a somewhat simpler structure, being similar in both jaws, and each
consisting of three slender, curved, and subconical cusps, separated by a pair of
rudimentary ones ; while there is an unpaired median series at the extremity of
the lower jaw only, instead of in both the upper and the lower. Although mainly
persistent, the notochord is in part replaced by ill-developed vertebrae of the type
characteristic of the suborder. Fossil teeth from the European Miocene have been
assigned to this genus.

THE SPINY DOG-FISHES AND THEIR ALLIES, Family SPINACID^:.

Although the members of the present family approximate in their external



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 56 of 62)