The Sea Turtles 



Hawk's-bill Turtle are examples of evolution from the 

 modern, fresh-water chelonians; development along the line of 

 adaptation to a strictly marine life has produced a highly spe- 

 cialised form, but the shielded carapace and plastron, and other 

 parts of the structure, show close relationship with the Tes- 

 tudinidce. Thus the student will appreciate that the family 

 Sphargidcs one species, and the Chelonidce four species, are not 

 alone widely separated in classification, but appeal to one an- 

 other only in a form that is essential to the life the species lead. 

 With this understood, it is not inappropriate to embrace all the 

 sea turtles in a chapter by themselves. This arrangement 

 popularises the subject and makes it possible to construct a 

 general key. 



KEY TO THE SEA TURTLES 



General: Limbs long, flat and paddle-like Flippers. 



A. Carapace with seven, heavy keels, running length- 



wise; covered with a leathery integument in place 



of shields. 



Uniform dark brown, or black. 



LEATHER-BACK TURTLE,' TRUNK TURTLE, SpharglS COriacea. 



B. Carapace covered with smooth shields, which do not 



overlap. 



*Front flippers with two claws. 



Head very large. Carapace uniform brown or black. 



Alveolar (crushing) surfaces of jaws without ridges 



under horny sheaths. 



LOGGERHEAD TURTLE, Thalassochelys caretta. 



Head very large. Carapace dark brown or black. Al- 

 veolar (crushing) surfaces of jaws with ridges under 

 horny sheaths. 

 KEMP'S LOGGERHEAD TURTLE, Thalassochelys kempii. 



**Front flippers with one claw. 



Head of moderate size. Carapace olive or brown, 

 mottled with yellow. 



GREEN TURTLE, Cbelonia mydas. 



C. Carapace covered with smooth, loosely-overlapping 



shields. 



Upper mandible beak-like. Carapace brown or black, 



mottled with yellow. 



HAWK'S-BILL TURTLE, Cbelonia imbricata. 



