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^e, 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 limbs 

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

 creature great swimming 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 with 

 whitewash. 



This creature has been considered to represent, so far 

 as its vertebral column is concerned, the primitive type 



