TURTLES, TERRAPINS, AND TORTOISES 13 



few constructing regular burrows which may extend to a 

 depth of several feet. 



The food varies according to the structure and the 

 mode of life. Land forms are vegetarians, those fre- 

 quenting the water are either carnivorous or herbivorous, 

 a few only living on a mixed diet. 



Tortoises are remarkably long-lived, the giant forms of 

 the Aldabra and Galapagos Islands attaining an age un- 

 paralleled by any other animal. 



The order is not a very large one, the number of species 

 of Chelonians amounting to only just over 200. 



Sub-order ATHEC^ : — Vertebrae and ribs free, within 

 the carapace. 



The Leathery Turtle, Dermochelys coriacea, of the 

 family Sphargid-s:, is the only representative of the sub- 

 order. It is the largest of living chelonians, and differs 

 from all other turtles, terrapins, and tortoises in its vertebrae 

 and ribs being entirely free, and not fused with the cara- 

 pace. The body is protected by a shield of small mosaic- 

 like bony plates, covered with a very thick layer of leathery 

 skin, which, except for the presence of a number of 

 longitudinal ridges, is in adult specimens perfectly smooth ; 

 in the young it appears rather tuberculate. The Hmbs 

 are paddle-shaped flippers, devoid of claws, giving the 

 creature great swdmming powers, and enabling it to ven- 

 ture far out to sea. In colour it is dark brown, often more 

 or less distinctly spotted with yellow, or as if splashed v^th 

 whitewash. 



This creature has been considered to represent, so far 

 as its vertebral column is concerned, the primitive type 



