TESTUDIXATA. 121 



spaces are raised into longitudinal ribs at intervals of from one to three 

 rows of pits. These ribs are equally developed at both ends of the costals. 



Measurements. 



M. 



Width of a costal bone uear middle 020 



Thickness of costal bone near middle 003 



The type specimen is smaller than that of the last. From Cottonwood 



Creek, Wyoming. 



Trionyx scutumantiquum Cope. 



Annual Report U. S. Geo. Geol. Surv. Terrs. 1872 (1873), p. 617. 

 Plate XVI, fig. 1. 



Established on a nearly perfect carapace and part of the plastron from 

 the bad lands of Cottonwood Creek. These indicate the largest species of 

 the genus yet found in North America. 



The carapace is a longitudinal oval, broadly rounded in front. The 

 median line forms a marked depression, and the costal bones rise and 

 descend again, forming an arch on each side. The free portion of the ribs 

 is not very long The sculpture consists of numerous honeycomb-like 

 pits separated by rather narrow ridges. On the middle parts of the carapace 

 these are subequal, but on the middle of the length of the costals all the 

 ridges run together longitudinally, and on their distal parts, these are broken 

 up so as to produce innumerable irregular tubercles and pits. The lines of 

 the intercostal sutures are smooth. Eight costal bones, and an anterior mar- 

 ginal coossified with the first costal by its entire width, and sending out a 

 broad costal extremity, which curves backwards, its anterior margin smooth. 

 Eight vertebrals, the last separating the anterior portions of the last costals. 



Measurements. 



M. 



Length of carapace 425 



Greatest width ot carapace, axial 410 



Thickness of fifth costal 0075 



Thickness of fourth vertebra 034 



Thickness of centrum of vertebra 010 



Several fragmentary individuals from the Wasatch beds, near Black 

 Butte, Wyoming, as also one from the corresponding formation on Bear 



