225 



variety of age, size, and condition of -preservation. Many exhibit in their 

 distortion evidences of considerable pressure, while others are so well pre- 

 served as to appear entirely unbroken. Their varied conditions, added to 

 slight anatomical variation, led me at first to attribute them to five different 

 species, which I now view as one. 



Mature specimens are comparatively rare, at least in an entire condition 

 One, broken into two pieces, is represented in Plate XXIII of "The Ancient. 

 Fauna of Nebraska." A second, more complete, was obtained by Professor 

 Hayden for the Academy of Natural Sciences of Philadelphia. 



Very few other bones of Stylemys nebrascensis, other than those of the 

 shell, have come under my notice. Among hundreds of shells and fragments 

 of others, I never met with any portions of the skull or jaws. 



Fig. 10, Plate XIX, represents a fragment of the scapula with part of its 

 precoracoid. It agrees with the corresponding portion of the bone in Testudo. 



Fig. 7, of the same plate, represents the distal extremity of a humerus of 

 a young individual. The hollow above the articular surface is rather deeper 

 than in Testudo. 



Stylemys niobrarensis. 



Numerous fragments of shells and a few portions of other bones of a 

 second species of Stylemys were discovered by Professor Hayden in the 

 Pliocene sands of the Niobrara River in the year 1857. All the anatomical 

 characters of the specimens indicate the same genus as the former, but 

 several of them point to a different species. It was about the same size as 

 the 8. nebrascensis. 



Fig. 4, Plate III, represents the anterior portion of a plastron of the 

 natural size, and therefore supposed to have belonged to a young animal. The 

 episternals are more prominent forward than in $. nebrascensis, and they arc 

 deeply excavated beneath the broad scute-covered margin, which is not the 

 case in the species just named. 



Fig. 5 represents the last vertebral and the pygal plates of an 

 older animal. It shows that the investing scute is single, as in Testudo. The 

 lower margin of the pygal bone is slightly but decidedly everted, which is 

 not the case in S. nebrascensis. 



Fig. 6 represents an inner view of a portion of a carapace one-half the 

 natural size. It belonged to a mature animal, and is the most complete por- 

 29 g 



