4 8o 



FOSSIL TURTLES OK NORTH AMERICA. 



of the species. Some of the specimens mentioned by that author are either not present or have 

 not been recognized. They had all been collected in the Bridger beds ot Wyoming. The type 

 came from Cottonwood Creek and therefore from level B, and has the American Museum's 

 number 3937, 



In the year 1903 the American Museum of Natural History sent a party into the Eocene 

 Badlands in the region of Fort Bridger, Wyoming. Among the materials collected by this 

 party is a nearly complete carapace and a fragmentary plastron, which are believed to belong to 

 the above species. These parts are represented by figs. 640 and 641. The specimen bears the 

 catalog number 5978. 



In form the carapace is oval, or elliptical, narrowed in front, rounded behind. It is con- 

 siderably archt, the midline rising to a height of "/I mm. above the borders. The length is 

 510 mm.; the width, 270 mm. The carapace (fig. 640) consists of a nuchal, 8 pairs of costals, 

 a preneural, and 6 neurals. The nuchal has a length of 145 mm. and a fore-and-aft width of 



641. 



Kigs. 640 and 641. Plastomenus aedenuus. Carapace anil plastron. 

 XJ. No. 5978 A. M. N. H. 



640. c 



arapace. 



641. Plastron. 



}X mm. along the midline. Its hinder border is somewhat excavated for the preneural. The 

 costals widen toward their distal ends. The free border of each is beveled. The free ends of 

 the ribs are very short. The thickness of the costals is about 5 mm. Those of the sixth pair 

 inclose between their proximal ends the sixth neural; but behind this they join in the midline. 

 The costals of the seventh and eighth pairs also meet in the midline, the former for a distance 

 of 20 mm., the latter for a distance of 65 mm. 



The preneural is pentagonal, 24 mm. long, and of about the same width. The first neural 

 is pentagonal, 25 mm. long and 19 mm. wide. The right postero-lateral side is very short, and 

 articulates with the second right costal. The third neural is four-sided, 34 mm. long and 16 mm. 

 wide. The next 3 neurals are hexagonal, with the narrow end forward. The fifth is 13 mm. 

 wide. 1 he last neural is small, 1 5 mm. long and 6 mm. wide. 



The sculpture of the surface consists of longitudinal ridges, or welts, and shallow pits. 

 Neither the welts nor the pits are conspicuous. The welts are obsolete on the anterior half of 

 the carapace, most distinct posteriorly. Running longitudinally as they do, they cross the cos- 

 tals of the middle of the carapace at right angles. Posteriorly thev cross the costals obliquely. 

 A close examination of the welts shows that they resemble those of the type of the species. On 

 the last costal they run in the same direction and become resolved into low tubercles, but these 

 are not so swollen as in the type. 



