154 



BAPTEMYS. 



A peculiar iiud interesting genus of extinct emydiform turtles, apparently 

 intermediate in its characters to the existing American genera Dermatemys 

 and Staurotypus, is founded on remains in the Bridger Tertiary formation of 

 Wyoming. 



In shape and constitution, the shell of Baptemys (Plate XII) approaches 

 most nearly that of Dermatemys^ more especially the carapace, while the 

 sternum partakes of the character of that of Staurotypus. 



The carapace is oval in outline, apparently not wider behind than in front, 

 and with the prominence or convexity about equal to half its breadth. The 

 convexity is nearly uniform fore and aft, and laterally to the flexure of the 

 marginal plates. The anterior border is bai'ely evei'ted and is thick and 

 rounded. The imperfection of the fossils prevents a determination whether 

 the posterior border departed from the general convexity of the liack of the 

 shell. The surface formed hy the first and second marginal plates is feebly 

 depressed. 



A median carina or thick rounded ridge starts upon the sixth vertebral 

 plate and extends backward. 



Eleven vertebral plates enter into the constitution of the carapace. Those 

 anteriorly are proportionately much longer than in emydes. They also appear 

 proportionately of greater extent than in Dermatemys. 



The first vertebral plate is oblong, somewhat narrowed behind, and with 

 the sides convex. Those to the sixth inclusive are hexagonal coffin-shaped. 

 From the fifth they rapidly decrease in length to the eighth inclusive, and 

 then increase again to the last. The seventh is niore uniformly hexagonal 

 than the others. The ninth is quadrate and wider than long. The tenth is 

 quadrate, widest behind, with the lateral borders convex and the back border 

 concave. 



Tlie costal plates arc like those of Dermatemys, and as in this widen out- 

 ■ wardly more than in ordinary emydes in accordance with the greater convexity 

 of the carapace. 



Tlie nuchal plate and marginal bones, so far as preserved, appear to be 

 nearly as in Dermatemys. 



The scute impressions of the carapace, as in the latter, are not defined by 

 such deep grooves as are usually observed in emydes. 



