TESTUDIISrATA. 129 



quite long-. The external borders of the latter are coarsely dentate, but 

 not digitate. The sculpture of the plastron is obsolete. 



The size of the Chelopus guttatus or Chysemys pidus of our streams. 



Specimens were found by myself and party on Cottonwood Creek, and 

 on the Upper Green River, Wyoming. 



EMYS Brong. 



The species of the Eocene formation which have been referred to this 

 genus are evidently members of the family Emydidce ; but owing to the 

 absence of descriptions and specimens of the crania, it is not certain to 

 which genus of the family they should be referred. As in similar eases in 

 paleontology, they are retained in the genus Emys until reasons for distin- 

 guishing them shall be discovered. 



As already remai-ked by Leidy, the species so referred, have left more 

 numerous remains in the Bridger beds than those of any other genus. The 

 same is true of the Green River and Wasatch formations, the genus Trionyx 

 only having left more abundant traces in the latter. During my explora- 

 tions in Wyoming, in 1872, I detected three species in the Wasatch and 

 Green River beds, one in the Washakie, and four in the Bridger formation; 

 in 1874 I obtained two species in the Wasatch strata. 



These species may be briefly distinguished in tabular form, as follows : 



I. The bridge sutures on not, or moderately, elevated axillary and in- 

 guinal buttresses. 

 a Dorsal line with projecting keel. 



Vertebral bones smaller, thicker U. polycypha. 



Vertebral bones larger, thinner; gular plates not reaching meso- 



sternal bone ; grooves moderate U. terrentris. 



Vertebral bones larger, thinner ; grooves very deep and wide .B. megaulax. 



a a No dorsal keel. 



i? Gular scuta not extending on mesosternum. • 



Bones massive, with lines of growth on some; costals swollen at 



proximal end of costal scuta U. testudinea. 



Bones thinner ; no lines of growth ; costal bones flat E. euthneta. 



yS ,3 Gular scuta extending on mesosternal bone. 

 y Vertebral bones wide. 



Shell thin ; lip of plastron not very wide H. lativertebralis. 



■f y Vertebral bones elongate. 

 Shell thin, little arched ; vertebral scuta wide ; sutures of plastron 



straight ; its lip narrower B. vyomingensU 



9 



