366 GEOLOGICAL SURVEY OF THE TERRITORIES. 



have been so rich in the number of genera and species relatively as 

 they do in the multitude of individuals of a few genera and species. 

 Their remains are found in association with the numerous mammalian 

 fossils of the mauraises terres of Dakota and those of the Niobrara 

 River. A greater number of species and genera are indicated by the 

 remains in the tertiary deposits of the vicinity of Fort Bridger, 

 Wyoming. 



EMYS. 



The genus ertiys includes many of our living fresh-water terrapenes, 

 and is also represented in Europe and Asia. It has latterly been divided 

 into different genera, founded on characters of the jaws, head, and feet; 

 so that from the fossil shells alone we are unable more distinctly to 

 define the animals. The shell of emys is rather oval in outline, mod- 

 erately convex. The sternum is large, truncated in front, and notched 

 behind. Its broad pedicles are joined by firm suture to the upper 

 shell or carapace. The outer portions of the humeral and abdominal 

 scutes cover these pedicles, and join the marginal scutes between the 

 X>osition of the axillary and inguinal scutes. 



Emys Jeanesi. — This species is founded on a nearly complete shell, 

 obtained, during Professor Hayden's last expedition, from the tertiary 

 deposit of the Bridger Group, near Fort Bridger, Wyoming. The length 

 of the shell, following the fore-and-aft curve, is fifteen inches ; the 

 length of the sternum is about one foot. The species is named in 

 honor of Joseph Jeanes, to whose aid we have been much indebted 

 in developing the fossil treasures of the West. 



Emys Haydeni. — A second species has been inferred to have existed 

 from an imperfect shell found in association with the former specimen, 

 together with many fragments of shells of the same and other species of 

 turtles. The species was about the size of the last, but is distinguished 

 from it by the difference of form of its scute impressions. 



Emys Stevensoni. — An apparent third species is founded on fragments 

 of the carapace and sternum of a shell, obtained by Dr. J. Van A. 

 Carter, from the tertiary deposit in the vicinity of Fort Bridger, 

 Wyoming. It has been named in honor of James Stevenson, the active 

 and efficient aid of Professor Hayden in his explorations. 



STYLEMYS. 



By this name the writer has distinguished an extinct genus of tur- 

 tles, which is intermediate in form between the modern land turtles 

 (Testudo) and the aquatic ones (Emys.) As in the former the back 

 extremity of the carapace is invested with a broad, symmetrical plate, 

 instead of a pair, as in the latter. 



Stylemys nebrascensis. — The species is established upon specimens 

 which have been collected by every explorer of the mauvaises terres of 

 White River, Dakota. So abundant have the'se fossil turtles been in 

 the locality mentioned that they have attracted the attention of the 

 most indifferent observers. Among the specimens submitted to the 

 examination of the author, considerable variation has been noticed, and 

 this variation at first led to the distinction of five different species. 

 At present he views them all as belonging to but one species. Several 

 mature specimens measure one and three-quarter feet in length by one 

 foot and a quarter in breadth. 



Stylemys niobrarensis. — A second species has been supposed to exist, 

 founded on a multitude of fragments, discovered by Professor Hayden 

 in association with mammalian remains in the pliocene sands of the 

 Eiobrara River. It was as large as the preceding species. 



