THE SUBCLASS ANAPSIDA 225 



Family Thalassemyidae. Temporal region of skull more or less 

 over-roofed. Neck short. Plastron loosely connected with carapace, 

 usually with one or more fontanelles. Ambulatory turtles. 



Upper Jura. Eurysternum Wagler, Thalassemys Riitimeyer, 

 Europe. 



Upper Jura and Wealden. Tropidemys Riitimeyer, Pelohatochelys 

 Seeley, Europe. Chitracephalus Dollo, Europe. 



Upper Cretaceous. Osteopygis Cope, Catapleura Cope, Lytoloma 

 (Rhetechelys, Erquelinnesia) Dollo, North America. Erquelinnesia 

 (Pachyrhynchus) Dollo, Europe, Africa. 



Eocene ?Lytoloma Cope, Europe. 



Family Toxochelyidae. Temporal region largely over-roofed. 

 Palatines entering into internal nares. Plastron loosely articulated. 

 Carapace with shields. Subaquatic, at least two claws on front feet. 



Cretaceous. Toxochelys Cope {? Cynocercus Cope), Porthochelys 

 Williston, North America. 



Family Desmatochelyidae. Skull almost wholly roofed over. 

 Internal nares far forward. Small palatine foramen. Nasals present. 

 Plastron loosely connected with carapace. Limbs paddle-Hke, 

 aquatic. 



Upper Cretaceous. Desmatochelys Williston, N eptunichelys Wie- 

 land, Atlantochelys Agassiz, North America. 



Family Protostegidae. Marine turtles of large size, the limbs 

 paddle-like without claws. Carapace greatly reduced, the plastron 

 loosely attached. Skull large; temporal region wholly roofed over. 

 Internal nares far forward, not under-roofed. 



Upper Cretaceous. Protostega Cope, Archelon Wieland, North 

 America. 



Family Cheloniidae. Marine turtles with paddle-like Hmbs and 

 elongate fingers. Skull mostly roofed over. Head not retractile. 

 Plastron loosely united to carapace. 



Upper Cretaceous. ? Allopleuron Baur, North America. Allopleu- 

 ron Baur, Europe. Peritresius Cope, North America. 



Eocene. Lemhonax Cope, North America. Argillochelys Lydek- 

 ker, Eosphargis Lydekker, Eochelone Dollo, Europe. 



Miocene. Scyllomus Cope, Procolpochelys Hay, North America. 



OHgocene. Chelyopsis Beedin, Europe. 



