EMYDID&. 287 
Dermatemydidz. The latter family was abundantly represented during the Upper Cretaceous 
and only slight modifications would be required to transform them into Emydida. 
In Europe the earliest Emydidz appear to be those found in the London Clay, which 
is of about the same age as the American Wasatch beds. Two species are found there; and 
these have been referred by Mr. Lydekker to Chr ysemys, a living North American genus. 
Doubtless when the skulls shall have been found these species will have to be relegated to some 
other genus. In the Oligocene of Hordwell, England, two species occur which Lydekker 
refers to Ocadra, a genus existing to-day in China. Te resembles closely the genus Echmatemys 
but the latter probably did not have a longitudinal ridge on the maxillary triturating cipiices 
and the plastron is less contracted than it is in Ocadza. No other species of Emydide have 
been discovered in England, so far as known to the writer. 
On the continent of Europe, as recorded by Maack (Palzontographica, xvill, 1869, p. 193) 
and by Zittel (Handbuch der Palaontologie, 11, p. 537), many species of Emydidz have been 
described and the greater part of them referred to Emys, Crstudo, and Ptychogaster. Only 
those called Cistudo are really members of Emys as now understood. This genus ‘thus appears 
to extend back to the Oligocene. Those placed by Maack and Zittel in die genus Emys are 
probably more closely related to Clemmys or Oc adia. Ptychogaster is an Oligocene and Lower 
Miocene genus, the carapace of which resembles in many respects that of Tasule, while the 
plastron is hinged like that of T errapene. 
The following table shows the distribution of the North American fossil species of the 
Emydide: 
Terrapene carolina, T. eurypygia, T. marnochi, Trachemys bisornata, T. petrolei, T. trulla, 
| Pleistocene. Equus. Chrysemys timida, Clemmys insculpta, Clemmys? percrassa, C. insculpta, ?Pseudemys 
celata. 
| Blanco, Terrapene putnami, ? Trachemys euglypha, T. sculpta, T. jarmani, ?Clemmys hesperia, Dei- 
‘ Rattlesnake, rochelys floridana, Pseudemys extincta. 
| Pliocene. q / , 
an 
Peace Creek. 
| Miocene. Loup Fork. Trachemys hill, Clemmys saxea. 
r - John Day 7 x : - 
| Oligocene. White River Graptemys inornata. 
| - - Uinta Echmatemys callopyge, E. uintensis. 
| Echmatemys septaria, E. ‘shaughnessiana, E. ocyrrhoe, E. stevensoniana, E. haydeni, E. 
Bridger. arethusa, E.naomi, E. cyane, E. egle, E. wyomingensis, E.? latilabiata, E. pusilla, Paleo- 
theca polycypha, Pp. terrestris, Clemmys morrisia, Hybemys arenaria. 
| Eocene. |——__|__ — E = 
| Wind River. 
| W asatch. Echmatemys lativertebralis, E. cibollensis, E. testudinea, E. megaulax, E. euthneta. 
| pene 
a Laramie. 
| Upp Fox Hills. 
Cretaceous. 
| 
Judith River. | >Gyremys spectabilis. 
Key To GENERA OF EMyYDID&. 
A. Insufficiently known genera. 
a‘. Carapace broad as long; the outer surface sculptured somewhat as in Tronychide. . Gyremys 
a’. Small Bridger species, with dorsal keel and thick bones .................... .... Paleotheca 
a®. A hemispherical boss situated on each interperipheral suture . Hybemys 
AA. Better known genera. 
Axillary and inguinal buttresses strongly developt; the latter projecting well into 
the cavity of the shell and rising high above the costo-peripheral suture Echmatemys 
Buttresses rising but little above the costo-peripheral sutures. 
Plastron without either lateral or transverse hinge. 
c. Crushing-surface of upper jaw with feeble or no longitudinal ridge. 
d', Humero-pectoral sulcus crossing the entoplastron .. Clemmys 
d°, Humero-pectoral sulcus crossing behind the entoplastron, 
