158 



fore and aft, it has measured about 20 inches in length, and the transverse 



arch from a level has been nearly as great. 



The length of the plastron has been about 11£ inches; its breadth from 

 its sutural junction with the carapace is 9 inches. 



The sides of the plastron slope inwardly to a moderate degree. The pedi- 

 cles are nearly on a level with the rest of the plastron, but are somewhat 

 prominent in front and slope backward, and are concave approaching the 

 inguinal fossa?. The rise of the shell appears mainly to commence in the 

 marginal bones from the sternal pedicles ; to what degree is uncertain, as 

 this part of the fossil is somewhat crushed inwardly. The rise is greater 

 anteriorly, and gradually appears to subside "behind. 



The fore and aft extent of the pedicles is 4^ inches. The length of the 

 anterior extension of the plastron has been about 3£ inches; its breadth at 

 the bottom of the axillary fossa? is b\ inches. The length of the posterior 

 extension of the plastron is a little more than 3^ inches, and its width at the 

 bottom of the inguinal fossae nearly 4^ inches. 



The marginal bones appear more abruptly bent to join the sternal bridge 

 than in Dermatemys, but the difference is partially due to the crushing 

 inward of the under part of the shell in the fossil. 



A second specimen of the shell of Baptemys wyomingensis was subse- 

 quently discovered during Professor Hayden's exploration of 1870 at Church 

 Buttes, Wyoming. The shell is of a different color, and is filled with and 

 partially imbedded in a different matrix from the former specimen. The 

 bones are brown, and the matrix consists of a very hard sandstone. The 

 specimen, though far less complete than the former, fortunately retains one- 

 half of the anterior part of the plastron. Most of the carapace is lost or 

 imbedded in the- hard rock. The sternum on one side from its fore extremity 

 to the commencement of the xiphisternal bone, together with the pedicle and 

 its characteristic scute impressions, is well preserved. 



The measurements of this second specimen indicate an individual of the 

 same size as the former. Slight differences existing between corresponding 

 parts of the two appear to be variations only of an individual character. In 

 the second specimen the large inguinal scute passes just over the back edge 

 of the hyosternal plate, while in the former one it extends upon it for half 

 an inch. 



