The True Sharks 193 
length. In the Upper Cretaceous is a very similar genus, 
Scapanorhynchus (lewis, 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. 
Mitsukurina, with Heterodontus, Heptranchias, and Chlamy- 
doselache, is a very remarkable survival of a very ancient form. 
Fic. 184.—Scapanorhynchus lewisi Davis. Family Mitsukurinide. Under side 
of snout. (After 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 Alopiide, or Thresher Sharks.—The related family of 
Alopiide 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 Pseudotriakide.—The Pseudotriakide consist of two 
species. One of these is Pseudotriakis microdon, a large shark 
