THE BLUE SHARK AND ITS ALLIES 2899 



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 mons- 

 ters. The blue shark has the whole of the upper parts slaty blue, and the under 

 surface white. 



Our next representative of the family is the small shark commonly 



known as the tope (Gateus cams), which belongs to a genus including 

 only two species and characterized 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 fin, 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 six feet in length, although it may grow to seven, 

 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 color it is dark gray 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 bot- 

 tom-haunting species especially during the winter months and devours other 

 fish, crustaceans, and starfishes. It is not unfrequently taken by the line, and is 

 thus a great source of annoyance to fishermen, 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 individ- 

 uals 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. 2896, form a genus unique among 

 fishes in the extraordinary conformation of the head. Instead of retaining 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 distinguish 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 fourteen or fifteen 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 



British sharks, one of which {Mustelus lams) is shown in the lower 

 figure of the following illustration. Externally these sharks are not unlike 

 the tope, but the snout is less pointed. As a genus they are characterized 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 fins. The teeth, more- 



