REPTILIA 



235 



It is believed by Dollo that Dermochelys is derived from an early 

 terrestrial thecophoran, which lost the primitive armature when it 

 assumed the completely marine habit; a belief that involves the idea 

 of reversed aquatic adaptation. Structurally the " leather-backs" 

 are so different from the other turtles that some authors advocate 



FIG. 133. Group of Chelonia, I. A, Leatherback Turtle, Dermochelys (Sphar- 

 gis) coriacea; B, Hawksbill Turtle, Chelone imbricata; C, Chelydra serpenlina 

 (Snapping Turtle) ; D, Pennsylvania Mud Turtle, Cinosternum pennsylvanicum ; 

 E, European Pond-Tortoise, Emys orbicularis; F, Carolina Box-Tortoise, Cistudo 

 (Terrapene) Carolina. (Redrawn after Lydekker.) 



putting them in a separate order. Recent discoveries, however, 

 have tended to confirm the conviction that they are an early aberrant 

 offshoot of a primitive land chelonian stock. 



SUB-ORDER II. THECOPHORA (TRUE TURTLES) 



The true turtles are subdivided into two assemblages: Cryptodira 

 and Pleurodira. 



