REPTILES 



217 



underlying ribs and vertebrae, besides which there is a complete 

 absence of overlying horny plates, the place of these being taken 

 by leathery skin raised into a small number of prominent longi- 

 tudinal ridges. The plastron is not so well developed as in 



Fig. 135. — Leathery Turtle {Dennatochelys coriacea.) 



ordinary turtles, and is covered by ridged skin resembling that 

 on the upper surface. These creatures are found in the tropical 

 parts of all the great oceans. 



(2) The S-necked Chelonia include the large majority of 

 existing species, and are so called because the head, when re- 

 tracted, is drawn straight back into the shell, being at the time 

 thrown into an S-shaped curve. 



{a) Land and Fresh-water Tortoises. — The genus Testudo 

 (figs. 134 and 136), to which the Grecian Tortoise (Testudo 

 Grcecd) belongs, is a representative of the largest family of Land 

 Tortoises, or indeed of Chelonia generally, including a score of 

 genera which embrace between them some 113 species. The 

 family is found in all parts of the world except Australia, New 

 Guinea, and the related islands. Among the most interesting 



