144 MEMOIRS OF THE CARNEGIE MUSEUM 



Hadrianus corsoni Cope, U. S. Geol. Surv. Terrs., 6th Ann. Rept., 1872 (1873), 

 p. 631; Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 450; Fossil Turtles 

 of North America, 1908, pp. 376-380, PI. LX, LXI; text-figs. 473-479. 



A large specimen in the present collection is identified as belonging to the 

 above genus and species, and represents the first recorded occurrence of Hadrianus 

 corsoni in the Uinta formation. This specimen consists of a complete plastron, 

 the peripherals of the right side above the bridge, and a few fragments of the cara- 

 pace. It was collected by 0. A. Peterson, August 5, 1912, six miles east of Myton, 

 Uinta County, Utah, from Horizon C of the Uinta formation, Upper Eocene. It 

 bears the C. M. Catalog No. 3403. 



The length of the plastron at the center is 740 mm.; the greatest length over 

 all 775 mm.; the greatest breadth about 490 mm. The posterior lobe is deeply 

 and widely notched and the anterior lobe is terminated in front by a wide spade- 

 like lip which projects prominently from the general contour of the lobe. 



Hadrianus corsoni was based upon the anterior portion of a plastron consisting 

 of the complete lip and lobe back to and including a small portion of the anterior 

 end of the entoplastron. A comparison of the specimen before me with the type 

 shows striking similarities in the contour of the lobe and lip, and especially of the 

 wide anterior end of the entoplastron, which appears peculiar to this species. The 

 lip has a transverse width at the base of 162 mm., which is greater than that of the 

 type, or of any subsequently discovered representative of this species. It projects 

 45 mm. beyond the point where the gular-humeral sulcus crosses the free border. 

 This measurement is slightly greater than in the type, but less than in the type of 

 Hadrianus octonarius Cope, now regarded by Hay as being a synonym of the 

 present species. The anterior border of the lip is subacute, nearly straight, but 

 slightly notched on the midline as in the type. The upper surface of the lip is 

 slightly convex along the midline, with shallow longitudinal depressions on either 

 side. The lower surface is flat, but I am inclined to believe it would have been 

 broadly convex in life. 



The anterior lobe is 345 mm. wide at the base, with a length of 252 mm. Along 

 the free borders on the upper surface the bone is bevelled off to an acute edge that 

 becomes obtusely rounded in front of the axillary notches. The lip on the superior 

 surface extends backward 67 mm. 



The entoplastron is unusually broad and angular in front. In the figures of 

 the type the suture Hmiting the anterior border of the entoplastron runs nearly- 

 straight across the median line, then turns abruptly backward and outward. In 

 the specimen here considered the anterior border is inclined more posteriorly, as 



