226 THE OSTEOLOGY OF THE REPTILES 



[Family Dermochelyidae. Leathery turtles. Marine turtles, 

 with mosaic of small, polygonal, bony plates, in the dermis of the 

 back, not ankylosed to the ribs. 



Eocene. Psephophorus, Egypt, North America. 



Recent. Dermochelys.] 



Family Chelydridae. Marsh and river turtles, with reduced plas- 

 tron loosely joined to carapace, the skull incompletely roofed. Ento- 

 plastron T-shaped. Caudals mostly opisthocoelous. Feet elongate, 

 webbed. 



Upper Jurassic. Tretosternum Owen {Peltochelys DoUo), Europe. 



Eocene. Gafsachelys Stefano, Europe. 



Miocene. ? Acherontemys Hay, North America. Chelydra, Europe. 



Pleistocene and Recent. Macrochelys Gray, Chelydra Schweiger, 

 North America. 



Family Dermatemyidae. Temporal region not roofed. Plastron 

 suturally united to carapace. No parietosquamosal arch. Caudals 

 procoelous. Marsh turtles, the carapace well ossified. 



Upper Cretaceous. Adocus Cope, Homorophus Cope, Zygoramma 

 Cope, Agomphus Cope, Compsemys Leidy, Basilemys Hay, North 

 America. 



Eocene. Anosteira Leidy, Baptemys Leidy, Pseudotrionyx Dollo, 

 Kallistira Hay, Notomorpha Cope, Alamosemys Hay, Basilemys 

 Hay, Hoplochelys Hay, North America. 



Ohgocene. Xenochelys Hay, ? Anosteira Leidy, North America. 

 Anosteira Leidy, Europe. 



Trachyaspis Meyer, Eocene, Miocene, Europe, Africa. 



Family Emydidae.^ Temporal region not roofed. Neck retrac- 

 tile. Carapace low-arched. Subaquatic, the feet webbed. Middle 

 digit rarely reduced. Marsh tortoises. 



Upper Cretaceous. ? Gyremys Hay. 



Eocene. Paleotheca Cope, Echmatemys Hay, North America. 

 ? Chrysemys, Emys, Europe. 



Oligocene. Graptemys Agassiz, North America. ? Clemmys Gray, 

 Europe. 



1 [Many modern taxonomists unite the Emydidae with the Testudinidae, as the 

 former grade into the latter. — Ed.] 



