246 



WATER REPTILES OF THE PAST AND PRESENT 



comes the name of the group — on the anterior digits, which are 

 used for burrowing in the mud and excavating holes for their 

 eggs. These turtles burrow more or less in the mud, with the long 

 neck free, lying in wait for their prey, and coming to the surface 

 from time to time to breathe. As the shape of the body and the 

 paddle-like feet would suggest, they are active swimmers and purely 

 aquatic in habit, never leaving the water unless compelled to. 

 They bur\- their hard-shelled eggs on the shores only a few feet 



from the water, and leave them to their 

 fate. If the pools in which they live dry 

 up, they burrow deeply in the mud and 

 await the rains and floods. In captivity 

 they feed upon all kinds of food, vegetable 

 as well as animal, and are active and 

 aggressive. 



Because of certain peculiarities, they 

 are usually classed in a separate suborder 

 all their own, the Trionychoidea, especially 

 distinguished from the Cryptodira, which 

 in general they resemble in most respects, 

 aside from the absence of the usual horny 

 dermal plates, in the lack of a marginal 

 row of bony plates around the carapace 

 — not a very important distinction. Less 

 than thirty living species are known, all 

 of them exclusively or chiefly of fresh- 

 water habit. Six species are known from 

 North America; the remainder inhabit 

 Africa, south of the Sahara Desert, southern India, and most of 

 the East Indian islands; none is known from AustraUa. No 

 species lives in South America and none is known to have lived 

 there in past times. During Eocene, Oligocene, and Miocene times 

 these fresh-water turtles lived in the region of Europe in great 

 numbers, but for some inexplicable reason they became extinct 

 there and never returned. Nearly seventy species of the Triony- 

 choidea, belonging in two families, are described by Dr. Hay from 

 the Tertiary rocks of North America, more than twice the number 



Fig. 130. — Aspidcretcs, a 

 trionychoid turtle from 

 the Basal Eocene of New 

 Mexico; skull from above. 

 (From Hay.) 



