Page:Encyclopædia Britannica, Ninth Edition, v. 21.djvu/803

Rh SHARK 777 to man ; at least, there is no instance known of a person having been attacked by the species common on the British coast (L. cornubica). It grows to a length of 10 feet, and ranges to New Zealand and Japan. See vol. xix. p. 518. To the genus Carcharodon particular interest is attached, because the single still existing species is the most form- idable 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 feet. The tooth figured here of the natural size (fig. 12) is taken from a jaw much shrunk in drying, but still 20 inches wide in its transverse dia- meter, and taken from a specimen 36 feet long. The extinct spe- cies must have been still more gigantic in bulk, as we may judge from teeth which are found in the crag or which have been dredged up from the bottom of the Pacific Ocean by the naturalists of the "Challenger" expedition, and which are 4 inches wide at the base and 5 inches long measured along their lateral margin. In some Tertiary strata these teeth are extremely abundant, so much so that for instance, in Florida the strata in which they occur are quarried to obtain the fossil remains for ex- port to England, where they are con- verted into artificial manure. The Fox-Shark or Thresher (Alopecias vulpes), of which every year specimens FIG. 12. Tooth of Carcharodon rondeletii. are captured on the British coast, but which is common in all the temperate seas of the northern and southern hemispheres, is readily recognized by its extremely slender tail, the length of which exceeds that of the remainder of the body. Its teeth are small, flat, triangular, and without serrature (fig. 1 3 ; the single tooth is of the natural size). It follows the shoals of herrings, pilchards, and sprats in their migrations, destroying incredible numbers and fre- quently injuring the nets by getting entangled in them. When feeding it uses the long tail in splashing the surface of the water, whilst it swims in gradually decreasing circles round a shoal of fishes which are thus kept crowded together, falling an easy prey to their enemy. Sometimes two threshers may be seen working together. Statements that it has been seen to attack whales and other large ceta- ceans rest upon erroneous observations ; its dentition is much too weak to bite through their skin, although, as Couch says, by one splash of its tail on the water it may put a herd of dolphins or porpoises to flight like so many hares. The same effect may be produced by the splash of an oar. The thresher attains to a length of 15 feet, the tail included. The Basking Shark (Selache maxima), sometimes erro- neously called "Sun-Fish," is the largest fish of the North Atlantic, growing to a length of more than 30 feet. It is one of the few types of sharks which up to a very recent time were considered to be peculiar to the North- Atlantic fauna ; but Prof. F. M'Coy has just recorded its occur- rence on the Australian coast, a specimen 30 feet long having been captured in November 1883 at Portland, on the west coast of Victoria. The mouth is of an extra- ordinary width, and, like the gill-cavity, capable of great expansion, so as to enable the fish to take at one gulp an enormous quantity of the small fish and other marine creatures on which it subsists. Ako the gill-openings are of great width. The teeth are very small, numerous, arranged in several series, conical, and probably without use in feeding. This shark is therefore quite harmless if not attacked. On the west coast of Ireland, where it is FIG. 13. Basking Shark. frequently seen during the summer months, generally in companies, at a distance of from three to a hundred miles off the shore, it is chased by the more courageous of the fishermen for the sake of the oil which is extracted from the liver, one fish yielding from a ton to a ton and a half. Its capture is not unattended with danger, as one blow from the enormously strong tail is sufficient to stave in the sides of a large boat. The simple method used at present of harpooning the fish entails much patience and loss of time upon the captors, as the fish generally sinks to the bottom and sulks for many hours before it rises again in a more or less exhausted condition ; and the use of more modern appliances could not fail of securing more speedy and better success. The basking shark is gregarious, and many individuals may be seen in calm weather lying together motionless, with the upper part of the back raised above the surface of the water, a habit which it has in common with the true sun -fish (Orthagoriscus), and from which it has derived its name. A shark similar in many points to the basking shark (which it exceeds in size), and an inhabitant of the Indo- Pacific Ocean, is Rhinodon typicus. In fact, so far as our present knowledge goes, it is the largest of all sharks, as it is known to exceed a length of 50 feet, but it is stated to attain that of 70. The captures of only a few specimens are on record, viz., one at the Cape of Good Hope, one or two near the Seychelles, where it is known as the "chagrin," one on the coast of California, arid one (quite recently) on the coast of Peru. The snout is extremely short, broad, and flat, with the mouth and nostrils placed at its extrem- ity ; the gill-openings very wide, and the eye very small. The teeth are, as in the basking shark, extremely small and numerous, conical in shape. No opportunity should be lost of obtaining exact information on this shark. The Greenland Shark (Lsemargus borealis) belongs to the XXI. 98