r^b The True Sharks 



length. In the Upper Cretaceous is a very similar genus, 

 Scapanorhynchus (lewisi, etc.), which Prof essor Woodward thinks 

 may be even generically identical with Mitsukurina, though 

 there is considerable difference in the form of the still longer 

 rostral plate, and the species of Scapanorhynchus differ among 

 themselves in this regard. 



Mitsukurina, with Heterodontus, Heptranchias, and Chlamy- 

 dosclachc, is a very remarkable survival of a very ancient form. 



Fig. .32S. — Scapajwrhi/nchiix leii-if;i Davis. Family Mitsukurinida: Under side 

 of .snout. (.AJter Woodward.) 



It is an interesting fact tliat the center of abundance of all 

 these relics of ancient life is in the Black Current, or Gulf Stream, 

 of Japan. 



Family Alopiidae, or Thresher Sharks. — The related family of 

 Alopiidcv contains probably but one recent species, the great 

 fox-shark, or thresher, found in all warm seas. In this species, 

 Alopias inilpcs, the tail is as long as the rest of the body and 

 bent upward from the base. The snout is verj^ short, and 

 the teeth are small and cLise-set. The species reaches a length 

 of about twenty-five feet. It is not especially ferocious, and the 

 current stories of its attacks on whales probably arise from 

 a mistake of the observers, who have taken the great killer, 

 Orca, for a shark. The killer is a mammal, allied to the por- 

 poise. It attacks the whale with great ferocitv, clinging to 

 its flesh by its strong teeth. The whale rolls over and over, 

 throwing the killer into the air, and sailors report it as a thresher. 

 As a matter of fact the thresher very rarely if ever attacks 

 any animal except small fish. It is said to use its tail in round- 

 ing up and destroying schools of herring and sardines. Fossil 

 teeth of thresher-sharks of some species are found from the 

 ]\Iiocene. 



Family Pseudotriakidse. — The Pscndolriakidcc consist of two 

 species. One of these is Psciidoiriakis inicrodoii, a laro-e shark 



