157 



marginal bone ; the inguinal fossa extends forward nearly on a line with the 

 posterior border of the sixth marginal bone. 



The interior of the fossils being occupied by the rocky matrix, all the 

 internal anatomical details are concealed from view. 



Baptemys in the relatively smaller size of the plastron to the carapace, and 

 in the presence of submarginal scutes to the sternal bridges, is more nearly 

 related to the marine turtles than the genus Emys. 



Baptemys- appears also to have been nearly related with the equally ancient 

 and extinct genus Pleurosternon, of the English Tertiary formation. In 

 this the vertebral scute areas of the carapace are remarkable for their breadth, 

 which considerably exceeds the length, whereas in Baptemys the intermediate 

 vertebral scute areas are much longer than broad. The plastron in Pleuro- 

 sternon is intermediate in its proportions to that of Emys and Baptemys, and 

 has an additional pair of bones entering into its composition which do not 

 exist in the latter genera. In Pleurosternon a pair of integular scutes inter- 

 vene to the gular scutes ; in Baptemys there appears to be no distinction of 

 gular scutes from humeral scutes. In Pleurosternon, as in Baptemys, large 

 accessory or submarginal scutes intervene to the comparatively large axillary 

 and inguinal scutes. 



Baptemys wyomingensis. 



The species thus named, as well as the genus, was first characterized from 

 a beautiful specimen of the turtle-shell, discovered by Mr. 0. C. Smith, of 

 Leverett, Massachusetts, while engaged in the service of the Union Pacific 

 Railroad Company, near Fort Bridger, Wyoming Territory. The specimen 

 was loaned to Professor Hayden, by whom it was sent to the writer for exam- 

 ination. It is represented in Plate XII, one-third the natural size. 



The specimen consists of a shell which nearly retains its original form, but 

 has lost the 1 front marginal plates on one side, all those behind, most of those 

 of the left, and the front part of the plastron. It is black, as is frequently 

 the case with the fossils from the same locality ; and it is filled in the in- 

 terior with a gray sandstone mingled with coarse pebbles of indurated bluish 

 clay. 



In its perfect condition the shell has measured about a foot and a half in 

 length, and in breadth about a foot. Following the curvature of the. carapace 



