133 



Buttes. It consists of the anterior extremity of the under shield or plastron, 

 consisting of the fore part of the episternals and the end of the entosternal. 

 The specimen might be supposed to belong to an Emys, but its resemblance 

 in form with the corresponding part in living species of Testudo leads me to 

 place it with this genus. The episternals project together rather abruptly 

 into a long, thick, and broad spade-] ike process, nearly straight at the front 

 border, but slightly notched at the middle. The projection behind is defined 

 by the outer extremities of deep grooves defining the gular and humeral scute 

 impressions. Its lower surface is strongly convex ; the upper surface slopes 

 forward to the acute border of the process. 



Back of the gular surface above, the plastron is deeply concave, but is not 

 excavated beneath the former as in the gopher, ( Testudo Carolina.) 



The end of the entosternal plate is impressed by the contiguous ends of the 

 gular scutes. The episternal process is about 2 inches long ; its breadth at 

 base is 5^ inches. The extremity of the process is 3f inches in width. The 

 thickest part of the episterna measures 1£ inch. 



The species I have named in honor of its discoverer, Dr. Joseph K. Corson, 

 United States Army, who to a love of his profession adds a special interest 

 in the promotion of the natural sciences. 



During my recent trip to Fort Bridger I was so fortunate as to obtain a 

 number of additional specimens referable to Testudo Corsoni. Some of them 

 had been previously collected by Drs. Corson and Carter, and others were 

 found during our explorations of the buttes near Fort Bridger, and those of 

 Dry Creek ten miles from the former. 



One of the best preserved specimens consists of a nearly complete ventral 

 shield or plastron, represented in Fig. 2, Plate XXX. This was discovered 

 by Dr. Corson at Grizzly Buttes, and presented by him to the Academy. In 

 the complete condition it has measured upward of 2 feet in length, and is 

 estimated to have been about 16 inches in breadth to its sutural conjunction 

 with the upper shell. 



In its form and proportions it resembles that of the living. Testudo radiala 

 of Madagascar more than it does that of the great Galapagos tortoise. 



The lobes of the plastron are of nearly equal length and breadth. The 

 prolonged extremity or spade-like process of the anterior lobe is lost in the 

 specimen. The posterior lobe terminates in a deep', wide, angular notch 

 included by two angular processes. 



The fore part of the anterior lobe is slightly bent upward and nearly straight 



