368 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



The carapace, or upper shell, is oval in outline, and resembles in shape 

 and constitution that of Bermatemys, a large, living fresh- water turtle of 

 South America. The plastron, or lower shell, partakes more of the char- 

 acter of that of Staurotygus. 



Compared with ordinary terrapenes, the intervals between the upper 

 and lower shells on each side are i3roportionately very large, more as in 

 the condition of the snappers. 



The bridges connecting the xjlastron and carapace are intermediate in 

 their proportions to those in Bermatemys and Staurotypus, and the same 

 may be said in relation with the common terrapenes and the snappers. 

 They are impressed by a row of three large scales between the position 

 of the usual scute impressions of the plastron and those of the border of 

 the carapace. 



The fore extremity of the plastron is nearly like that in Bermatemys, 

 but is widely emarginate at the end, and is obtusely rounded at the border 

 instead of being acute as usual in terrapenes. The hinder extremity of 

 the plastron is narrower proportionately than in Bermatemys, but wider 

 than in Staurotypus, and it ends in a rounded manner. 



The first pair or gular scute impressions of the plastron as existing in 

 ordinary terrapenes appear to be absent in Baptemys, or rather they are 

 not distinct from the humeral scute impressions. 



The shell of Baptemys wyomingensis is about 1^ feet in length and 1 

 foot in breadth. The plastron is rather less than 1 foot iu length ; its 

 breadth to its junction with the carapace 9 inches j and the fore and aft 

 extent of its bridges 4J inches. 



Baptemys is nearly related to the extinct genus Pleurosternon of the 

 English Tertiary. 



Baena. 

 - Baena arenosa. 



The extinct genus of turtles, Baena, was origin allj'^ indicated by a 

 nearly complete shell, discovered during Prof. Hayden's expedition 

 of 1870, in the vicinity of Fort Bridger, Wyoming. Another shell, dis- 

 covered by Dr. Carter in the same locality, and i)resented to the writer, 

 from some variation, was supposed to indicate a second species of the 

 same genus. The two were named Baena arenosa and B. affinis. Addi- 

 tional specimens exhibiting some variation of character lead me to 

 suspect that these are the same. 



The specimens generally have been so much crushed downward that 

 it is difficult to form an estimate of the degree of convexity or promi- 

 nence of the shell of Baena arenosa. It would appear to be rather com- 

 pressed, or about as prominent as in the ordinary Snapi)er. It partakes 

 of characters of the latter, the terrapenes, and the sea-turtles. 



In all the specimens the bones which compose the shell are completely 

 co-ossified, so that the sutural connections cannot be followed. 



The upper shell is broadly oval, and is notched behind as in the Snap- 

 per. The under shell is flat and more like that of a terrapene in 

 appearance than that of the Snapper. The bridges connecting the two 

 shells are relatively as wide as in the former but are longer. The ends of 

 the plastron are tongue-like and feebly emarginate. 



The number and arrangement of the horny scales of the carapace 

 appear to be the same as in the terrapenes and snappers. The scales 

 of the plastron consist of seven i)airs, besides additional ones to the 

 bridges, as in the latter and the sea-turtles. 



The shell of Baena arenosa was a little over a foot in length and three- 

 fourths of a foot in breadth. 



