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, Leatherbaok Turtle, Dermochelys {Sphar- 

 gis) coriacea; B, Hawksbill Turtle, Chelone iinhricata; C, Chelydia nerpenlina 

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

 E, European Pond-Tortoise, Eiiiys orbicularis; F, Carolina Box-Tortoise, Cidudo 

 (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. 



