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 Rütimeyer, Europe.
Upper Jura and Wealden. Tropidemys Rütimeyer, Pelobatochelys 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-like, aquatic.
Upper Cretaceous. Desmatochelys Williston, Neptunichelys Wieland, 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 limbs and elongate fingers. Skull mostly roofed over. Head not retractile. Plastron loosely united to carapace.
Upper Cretaceous. ? Allopleuron Baur, North America. Allopleuron Baur, Europe. Peritresius Cope, North America.
Eocene. Lembonax Cope, North America. Argillochelys Lydekker, Eosphargis Lydekker, Eochelone Dollo, Europe.
Miocene. Scyllomus Cope, Procolpochelys Hay, North America.
Oligocene. Chelyopsis Beedin, Europe.
