536 The True Sharks 



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

 Scapanorhynchus (lewisi, etc.), which Professor 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. 



Mitsukurma, with Heterodontus, Heptranchias, and Chlamy- 

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



FIG. 328. Scapanorhynchus lewiRi Davis. Family Mitsukurinidce. Under side 

 of snout. (Alter Woodward.) 



It is an interesting fact that 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 

 Alopiida contains probably but one recent species, the great 

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

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

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

 the teeth are small and close-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 ferocity, 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 

 Miocene. 



Family Pseudotriakidae. The Pseudotriakida consist of two 

 species. One of these is Pseudotriakis microdon, a large shark 



