B ASKING-SHARKS. 527 



which more than half is taken up by the tail, this shark has the second dorsal and 

 anal fins very small ; the caudal fin 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 be 

 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 

 are 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 

 ' 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 west 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 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. Kemains of an extinct species 

 occur in the Pliocene deposits of Belgium, while others from older Tertiary beds 

 have been tentatively assigned to the genus. 



INDO-PACIFIC BASKING-SHARK, Family RHINODONTIDJS. 



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 



