158 MEMOIRS OF THE CARNEGIE MUSEUM 



The first neural is exceedingly large, being 93 mm. long and 50 mm. wide toward 

 the front. The others present diminish in size posteriorly. The second, third, 

 and fom-th are coffin-shaped, with the widest end posterior, as is usual in the species 

 of this genus. The principal dimensions of the neurals are given in the table. 



No. Length. Width. 



1 93 50 



2 62 41 



3 59 38 



4 58 34 



All of the costal plates except the first grow wider toward their outer ends. 

 The expansion of the outer end of the second, as in the type, is especially pronounced. 

 In the angulation of the free border of the second costal it resembles that of Amyda 

 salebrosa Hay, more nearly than the type of the present species. At their free ends 

 all of the costals preserved are bevelled off to a sharp edge, except at the point 

 where the rib projects. None of the projecting ribs are preserved, so that the 

 distance they extend beyond the free border cannot be determined. Near their 

 outer ends at the sutural borders the costals have a thickness of from 5 to 9 mm. 

 The width of the proximal and distal ends of the costals are given in the table. 



No. Width of Proximal End. Width of Distal End. 



1 91 62 



2 58 103 



3 63 79 



4 58 79 



5 59 84e 



e, estimated. 



The surface of the carapace is ornamented with the usual pits and ridges, there 

 being two pits in a line 10 mm. long, and occasionally three. They are large and 

 distinct, forming a honeycomb arrangement along the middle and on the proximal 

 halves of the costal plates, becoming smaller and less deeply impressed toward the 

 front. In small areas here and there at points about the middle of the costals the 

 pits are arranged in rows across the short diameters of the plates. On the distal 

 portions of the costals the pits are smaller and less deeply impressed, thus forming 

 a very distinct pattern, and, as the smooth band is approached, the ridges show a 

 tendency to break up into tubercles. Nowhere are the ridges wider than the pits. 



Except for the considerably greater size of the specimen, and slight differences 

 in the general distribution of the large and small pits the present individual agrees 

 very closely with the type. The latter is from the Bridger beds on Cottonwood 



