lOO 



reference cannot be certain, as the specimens described 

 and figured by Professor Cope have the crowns of the teeth 

 broken. The tooth is not so long as the largest tooth of P. 

 inoiossns, but is of proportionately greater diameter and not 

 so straight. It is conical and recurved, and shows two very 

 obscure cutting-edges, which divide the crown into two un- 

 equal faces. It has famt longitudinal striations on all sides, 

 and the apex is sharp. 



Measurements. 



M. 



Fore-and-aft diameter at the base 0-613 



Height of crown 0-020 



NEMATOGNATHI. 



SILURIDyE. 



" Skin naked, or with osseous scutes, but without scales. 

 Barbels always present; maxillary bone rudimentary, margin 

 of the upper jaw formed by the premaxillaries only. Subo- 

 perculum absent; adipose fin present or absent." (Gunther.) 



RHINEASTES, Cope. 



U. S. Geol. Survey of the Terrs., 1872, p. 63S. 



A genus allied to the recent IcJitluvlnrus but differing in 

 the inferior grooving of the vertebras and in the rough exos- 

 toses of the cranial bones. It differs from Phareodon in having 

 the usual band of bristle-like teeth on the dentary. 



Rhineastes ? 



Represented by a portion of the dentary and hyomandi- 

 bular bones of a large cat-fish from Bridger Butte. 



The dentary is broad and shallow, grooved below, and 

 deeply striated on the external face. As much of it as is pre- 

 served is straight. The teeth are small, subequal through- 

 out, and very numerous. The hyomandibular is broad and 

 thick, and has a striated surface. The condyle is peculiar in 

 having two separate articular faces above and below, one 

 convex andthe other flat. 



