P^RT FIRST. 



THE WASATCH AND BRIDGER FAUN^. 

 PISCES. 



The remains of fishes are abundant in the lacustrine Eocene forma- 

 tions of the United States, and several principal groups are represented. 

 These pertain to the Elasmohrancld and the Hyopomata ; Dipnoi and Holoce- 

 phali are unknown. Of Hyopomatous fishes, indications of the Crossop- 

 terygia and the Chondrostei have not yet been found, but of the third group, 

 the Actinopteri, we have several distinct orders, commencing with the more 

 generalized Ginglymodi and ending with the specialized Percomorphi. The 

 facies of the Eocene fish fauna is that of the existing fresh waters of the 

 United States, exclusive of the great order of the Plectospondyli (unless the 

 Amyzon beds are Eocene), and with the addition of two families, Osteoglos- 

 sidee and Chromididee (aff*.), at present confined to the southern hemisphere. 



ELA8M0BRANCHL 



XIPHOTRYGON Cope. 



American Naturalist, 1879, p. 333. 



Family Trygonidce; that is, the tail furnished with a seiTate spine and 

 the pectoral fins united in front of the rostral cartilage. Teeth closely 

 placed in a few rows, the crowns developed into a triangular cusp, which 

 is directed backwards, as in Raja. Pelvic arch without anteriorly directed 

 inferior processes. No superficial ossification of the rostral cartilage. No 

 caudal fins observed. 



This genus is Trygon, with the teeth of Raja. It further differs strik- 



4 49 



