THE SUBCLASS ANAPSIDA 227 



Miocene. Trachemys Agassiz, Clemmys Ritgen, North America. 



Pliocene. Terrepene Merrem, Trachemys Agassiz, ? Clemmys Rit- 

 gen, Deirochelys Agassiz, Pseudemys Gray, North America. 



Pleistocene. Terrepene Merrem, Chrysemys Gray, Clemmys Ritgen, 

 ? Pseudemys, North America. 



Ptychogaster Pomel, Oligocene, Miocene, Europe. 



Family Testudinidae. Temporal roof reduced. Neck retractile. 

 Plastron suturally united with the highly arched carapace. Pha- 

 langes not more than two in number. Small to very large tortoises, 

 herbivorous, terrestrial. 



Eocene. Hadrianus Cope, Achilemys Hay, North America. Tes- 

 tudo, Africa. 



Oligocene. Testudo Linne, Stylemys Leidy, North America. 



Miocene to Recent. Testudo Linne, North America, Europe, 

 Asia, Africa. 



D. SUBORDER TRIONYCHOIDEA 



Skull and neck as in the Cryptodira, the basiphenoid separating 

 the pterygoids. Plastron ligamentously united with carapace, which 

 lacks the peripheral bones and is covered with a leathery skin only 

 and is flattened. More than three phalanges in third digit. River 

 and lake turtles, the neck long. 



Family Plastomenidae. Hyoplastra, hypoplastra, and xiphi- 

 plastra closely united. Legs unknown. 



Uppermost Cretaceous and Lower Eocene. Plastomenus Cope, 

 North America. 



Family Trionychidae. Openings between hyoplastra, hypo- 

 plastra, and xiphiplastra. Three claws only, feet elongate. 



Uppermost Cretaceous. Helopanoplia Hay, North America. 



Eocene. Cotichochelys Hay, Axestemys Hay, Aspideretes Hay, 

 Amyda Oken (= PlatypeUis Fitzinger), North America. 



