51 



floor of the large orbit. The mandible is slender and com- 

 pressed, with a large dental canal. 



The atlas is small, and has narrow transverse processes, 

 which are perforated b}^ a large vertebraterial canal. The 

 dorsals have considerably depressed centra, and the ribs are 

 slender. 



Length of last molar.. 

 Breadth of last molar. 



Measurements. 



M. 



025 



030 



Length of second molar .024 



Width of second molar -0305 



Length of last (?) premolar .018 



Width of last premolar . -0245 



Length of second lower molar .025 



Width of second lower molar .018 



From Henry's Fork Divide. 



Hyrachyus LNTERMEDIUS, Sp. nov.. 



Established on the upper true molar series of the righ: 

 side. 



This species is intermediate in size between H. agrariii ? 

 and H. modestus. As in the latter species; the basal ridge ex . 

 tends around the entire crown of the tooth, with a small in. 

 terruption on the antero-external lobe. It is more pronounced, 

 in front and less behind than in H. iuipei-ialis. The anterior 

 conical buttress is not nearly so well developed as in H. impe^ 

 I'ialis ; the valleys are wide, and the descending fold from 

 the antero-external lobe is obscure, scarcel}^ marked at all in 

 the first. The transverse crests are strongly arched forwards, 

 and the anterior is very much the longer. The peculiar fea> 

 ture of the species is the position of the postero-externa , 

 lobe, which is pushed to the posterior aspect of the tooth ; 

 this is carried so far in the last molar that the two external 

 lobes stand on nearly the same transverse line. The antero- 

 external lobe is much the highest point in the tooth, and i'?. 

 the first molar is remarkably sharp. The enamel is consider • 

 ably wrinkled, but not nearly so much as in H. modestus. 



