THE CARTILAGINOUS FISHES 217 



the common Tope a " Rig," Spiny Dog-fish are " Spur-dogs " in the 

 vernacular of the fisherfolk ; and a species of Tope with a long, 

 projecting snout often goes by the name of " Old Shovel-nose " 

 among them. 



One of the commonest of the larger sharks seen in British waters 

 is the Fox-shark, or Thresher (Alopecias wipes). It has gained 

 its first popular name from its long, curved tail, or caudal fin, 

 which is supposed to bear some sort of resemblance to a fox's 

 brush ; while the curious way it has of beating the water with that 

 appendage is responsible for its second name of " Thresher." This 

 shark grows to about 15 feet, but quite half its length is taken 

 up by its long tail-fin, so that it is not really of a very large size. 

 It feeds on herrings, pilchards, and other small fishes, following the 

 shoals and devouring extraordinary numbers of individuals. When 

 hunting, the Thresher swims round and round the shoal, drawing 

 gradually nearer to the fishes, which huddle together in a mass. 

 While going through these manoeuvres the shark keeps up a con- 

 stant splashing in the water with its long tail in order to frighten 

 and drive its victims to the centre of the circle, where, crowded 

 one upon another, they fall an easy prey. 



The Greenland Shark (Lamargus borealis) is occasionally cap- 

 tured off the coasts of Great Britain, for, although its natural 

 haunts are in the Arctic regions, this shark, like many of its allies, 

 is a great wanderer, and sometimes ventures as far southwards 

 as the coast of France. It reaches a length of 26 feet, and is a 

 bulky, clumsily built fish, with very small fins. It feeds to a 

 great extent upon the " right" whales, and is said to attack them 

 with great ferocity, biting large pieces out of their bodies with 

 its small but strong, sharp teeth. 



The Hammer-head Sharks (Sphyrnides) are distinguished by the 

 extraordinary shape of the head, which is drawn out on each side 

 into a conspicuous lobe, and has a striking resemblance to a 

 hammer. The shape of the head varies somewhat in different 

 species, of which there are five ; in one, called the " Bonnet Shark," 

 the projecting lobes are rounded, forming a crescent-shaped head- 

 piece suggesting an old-fashioned poke bonnet. These sharks are 

 denizens of nearly all the tropical and subtropical seas, but often 

 wander into more temperate waters, and specimens are occasion- 

 ally captured off our coasts. They are large fishes, frequently 



