The genus was first named by Edward Drinker Cope in 1867, and contains three species.

[4][5] Unlike the sea turtles Toxochelys and Eochelone, Euclastes has a secondary palate.

[6] The genus can be distinguished by later sea turtles based on its broad, low skull; broad, flat palate; wide, flat dentary bone with an elongated symphysis; and low tomial ridge on the beak.

The widened palate and dentaries give Eochelone wide, flat jaws suitable for crushing hard-shelled organisms.

[3] Cladogram based on Lynch and Parham (2003)[3] and Parham and Pyenson (2010):[7] Toxochelys Mexichelys Lophochleyinae Euclastes Argillochelys Eochelone Erquelinnesla Pacifichelys Puppigerus Cheloniidae sensu stricto Fossils of Euclastes have been found in:[8]