Page:EB1911 - Volume 24.djvu/839

Rh Pelagrk Sharks.—All these are of large size, and some are surpassed in bulk and length only by the larger kinds of cetaceans. FIG. 8.-Egg-shell of same fish. I:, External view; a and b, the two spiral ridges; c, cavity for the ovum.. II., section;

Those armed with powerful cutting teeth are dangerous to man, whilst others, which are provided with numerous but very small teeth, feed on small fishes only or marine invertebrates, and are of a timid disposition, which causes them to retire into the solitudes of the open sea. On this account we know very little of their life. All pelagic sharks have a wide geographical range, ' and nearly all seem to be viviparous.

Of the more remarkable forms which we propose to notice here the genus most abundantly represented in species and individuals is Carcharias, now split up by 'many authors into several separate genera. Perhaps nin e-tenths of the sharks of which we read in books of travel belong to this genus. Between 7¢.?»3Q CY K r

FIG. 9.-Teeth of

A canthias vulgaris.

QM I

FIG. ro.-Dentition of the Blue Shark (Carcharias glaucus). The single teeth are of the natural size. thirty and forty species have been distinguished, all of which are found in tropical seas. They are the sharks which so readily attach themselves bo sailing vessels, following them for weeks. Others affect more the neighbourhood of land. One of the most common species is the blue shark (Carcharias glaucus), of which specimens (4 to 6 ft. long) are frequently caught on the S. coastS of England and Ireland. Other species of Carcharias attain a length of 30 ft. The mouth of all is armed with a series of large fiat triangular teeth, which have a sharp, smooth or serrated edge (fig. ro).

Galeocerdo is likewise a large shark very dangerous to man, differing from the preceding chiefly by having the outer side of its teeth deeply notched. It has long been known to occur in the N. Atlantic, close to the Arctic Ocean (G. arclicus), but its existence in other parts has been ascertained within a recent period; in fact, it seems to be one of the most common and dangerous sharks of the Indo-Pacific, the British Museum having obtained speci- ~. mens from Mauritius, Kurrachee, Madras and the W. coast of Australia.

Hammerheaded sharks (Sphyrna-Zygaena) are sharks in which the anterior FIG. 'I I' U per and portion of the head is produced into aLower Tooth oi)Lamna. lobe on each side, the extremity of which is occupied by the eye. The relation of this unique configuration of the head to the economy of the ish is unknown. Otherwise these sharks resemble Carcharias, and ara? equally formidable, but seem to be more stationary in their habits. They occur in all tropical and subtropical seas, even in the Mediterranean, where S. Zygaena is by no means rare. In the Indian Ocean it is common, and Cantor states that specimens may be often seen ascending from the clear blue depths of the ocean like a great cloud.

The p orb eagles (Lamna) differ from the preceding sharks in their dentition and are not dangerous to man; at least there is no instance known of a person having been attacked by the species common on the British coast (L. wfnubica). This is.refe1'red to in the works of older British authors as “Beaumaris shark? The short and stout form oi

its body contrasts strikingly

with its much attenuated

tail, which, however, is strengthened by a keel on each side

and terminates in a large and

powerful caudal fin. The

snout is pointed, and the jaws

are armed with strong lanceolate teeth, each of which bears

a small cusp on each side of

the base (see fig. rr). The

teeth are not adapted for cutting, like 'the flat triangular

teeth of man-eating sharks,

but rather for seizing and

holding the prey, which consists chiefly of various kinds

of fishes and cephalopods. In

the upper jaw there are from

thirteen to sixteen teeth on

l.

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AHJ, ,/ ss.., I

X

v

n

f ', ¢ -"""  'V "f It

" / '1 ~

1,

(» . /I, g»¢'? "'s§ - ~, it

Wal//{ I f/ I" ' 'l

mt' we

f 4

FIG. 12.-'I'ooth of Cll1GhG1'0d01$'~ » rondeletii. . »each

side, the third being remarkable for its small size; the “ lower Jaw from twelve to fourteen. The gill-openings are wide. The p orb eagle attains to a length of ro or 12 ft., ';and is a pelagic fish, not rare in the N. Atlantic and Mediterranean, and frequently wandering to the British and more rarelyto tlié American shores. This species is widely distribLfted ovei" the N, of the Atlantic and Pacific Oceans. Other- closely allied, species (L. spallanzanii, L. glauca) are known to occur in the S. Atlantic, from the Mediterranean to the Cape of Good Hope. ' A f To the genus Carcharodon particular interest is attached, because the single still existing species is the most 'formidable of all sharks, as were those which preceded it in Tertiary times. The existing species (C. rondeletii) occurs in almost all tropical and subtropical seas, but seems to be verging towards extinction. It is known to attain to a length of 40 ft. The tooth figured