310 CLASSIFICATION OF VERTEBRATES. 



tropics the terrestrial species sleep through the dry season. 

 The group appears in the Permian of North America, and has 

 continued until the present. 



Sub-Order i. Chelydosauria. 



No temporal fossa ; carapace of transverse osseous arches in close con- 

 tact, extending across tiie back from side to side. Vertebrae ampliicoelous ; 

 limbs ambulatory. This .sub-order, represented by Otoccehis from the Per- 

 mian of North America, is regarded by Cope as ancestral to the other 

 chelonia and the pseudosuchian crocodilia. 



Sub-Order 2. Athec^. 



Turtles without scales but with a leathery skin, carapace of polygonal 

 dermal bony plates arranged in rows, unconnected with ribs and vertebras ; 

 plastron poorly developed, with large central fontanelle ; episternum lacking. 

 Skull without descending process of parietals. Feet flipper-like, claws lack- 

 ing. Dermochelys {Sphargis) coriacea, the leather-back tortoise, occurs 

 in all warmer seas, extending north to Cape Cod. It weighs occasionally 

 1.500 lbs. The sub-order appears (^Psephodermd) in the trias. Proiostega, 

 cretaceous of Kansas. 



Sub-Order 3. Trionychia. 



Turtles with the carapace poorly ossified, ribs and vertebrae being 

 connected with it. Scales lacking, the body covered with a leathery skin ; 

 marginal bones few or absent. Plastron with episternum and a large me- 

 dian fontanelle ; sacral and caudal ribs articulating with neural arclies. 

 A descending process of the parietals present. Feet webbed, three claws 

 on each foot. The sub-order appears in the upper cretaceous of New 

 Jersey, and is represented by over thirty species to-day, all inhabitants of 

 fresh water, and best developed in the Oriental regions. All are carnivor- 

 ous. Four species of leather turtle (Aiiiycfa) and soft-shell turtles (As- 

 ■pidonectes) in the U. S. 



Sub-Order 4. Cryptodira. 



Turtles with well-ossified carapace, connected with internal skeleton; 

 epidermal scales and marginal ossicles present ; an episternum ; pelvis free 

 from plastron; caudal ribs articulated to vertebral centra. .\ descending 

 process to the parietals. The species are numerous, the more important 

 families being the following: Chelonid.e, with heart-shaped carapace, and 

 paddle-like feet, bearing at most two claws. The costal plates do not 

 reach the marginals. Thalassochelys caretta, the loggerhead turtle, weighs 

 450 lbs. Eretmochelys imbricata, the tortoise-shell turtle, is smaller. The 

 green turtle, Chelone mydas, may weigh 850 lbs. It is highly esteemed as 



