6 REPTILES OF THE WORLD 



for placing this turtle in a suborder by itself is because 

 the vertebras and ribs are not rigidly attached to the 

 carapace as with all other chelonians. The carapace and 

 plastron are actually composed of a large number of 

 irregularly-shaped plates; except where these protrude 

 — on the upper shell — in the shape of keels, or heavy 

 ridges, they are imbedded in the oily, fatty substance, 

 like whale blubber, that externally presents a leathery 

 appearance and suggests a popular name for the ani- 

 mal. 



Like the other marine turtles, the present reptile dif- 

 fers from other chelonians — the fresh-water species — 

 in having the limbs developed into huge, seal-like "flip- 

 pers" or paddles. Yet the appearance of the limbs and 

 head is quite different from corresponding parts of the 

 structure of the well-known Green Turtle and the Log- 

 gerhead Turtle : for with the present reptile these mem- 

 bers are not, on mature individuals, covered with shields 

 or plates; the dark, smooth skin of the head and the 

 enormous bare flippers are characters strikingly sug- 

 gestive of a seal. 



If this turtle is to be compared with the four species 

 that make up the family Chelonidce — the Green Turtle, 

 Hawk's-Bill Turtle, and two species of Loggerhead 

 Turtle, gross examination might point to a general simi- 

 larity of structure. It is true that the Leathery Turtle 

 and the other sea turtles have much the same paddle- 

 like limbs, but this similarity in development merely sig- 

 nifies the process of evolution along similar lines in two 

 widely-separated groups; it is an admirable example of 

 adaptation. Incidentally, it might be explained that the 

 species composing the Chelonidce appear to be highly 

 specialized forms that have originated from the Testu- 

 dinidce, while the Leathery Turtle represents ancestral 



