220 CHARACTERS OF VERTEBRATE ANIMALS 



hotter parts of Asia, Africa, and North America, their name 

 being derived from the fact that the shell is entirely devoid of 

 any horny plates. Not only so, but the carapace is deficient as 

 regards bony elements, the marginals being either absent or 

 largely so, and it is not united to the plastron, which is still more 

 deficient. The shape of the body and limbs accords with the 

 thoroughly aquatic habit, but the latter are not so completely 



Fig. 137. — Nilotic Soft Tortoise ( Trionyx triun^is) 



converted into flippers as in the turtles. The head is provided 

 with a curious tapering snout, and is situated upon a very long 

 mobile neck, which on the one hand can be retracted as in the 

 S-necked forms, and on the other can be shot out with extreme 

 rapidity. This is, no doubt, a useful acquisition to the large 

 carnivorous members of the group, but is at the same time a 

 very unpleasant one, for these large species are very fierce, and 

 the natives are often badly bitten by them. The skin is of a 

 greenish colour as a rule, with yellow spots. 



Of the six genera included among the Soft Tortoises, Trionyx 

 is by far the most important and also the most widely distributed. 



