67 



worn and perfect specimen, and agrees in its anatomical characters with the 

 corresponding tooth of H. agrarius. The crown measures an inch antero- 

 posterior^ and 7£ lines transversely. 



The specimens above described indicate an animal about the size of the 

 common American tapir. 



Hyrachyus modestus. 



Under the impression that teeth of like form with those of Hyrachyus 

 agrarius, from the Bridger Tertiary formation, pertain to the same genus, I 

 now view the tooth represented in Fig. 13, Plate II, which I previously 

 referred to Lophiodon modestus, as belonging to Hyrachyus. The specimen 

 was obtained during Professor Hay den's exploration of 1870, on Smith's Fork 

 of Green River, near Fort Bridger. 



The tooth is a first or second upper molar, and differs in size and propor- 

 tion from the corresponding teeth of Hyrachyus agrarius sufficiently to indi- 

 cate a smaller species. The only other difference observable, one, however, 

 which may prove not to be constant iu additional specimens, is in the internal 

 surface of the antero-internal lobe of the crown, being strongly wrinkled in- 

 stead of being elevated in a single conspicuous fold as in H. agrarius. 



The comparative measurements of the specimen are as follows: 



Diameter fore and aft of second upper molar. 

 Diameter transversely of second upper molar. 



Hyrachyus modestus was about a third less in size than H agrarius. ■ 



Hyrachyus nanus. 



Portions of two lower jaws I have referred to a small species of Hyrachyus 

 with the above name. One of the specimens was obtained at Lodge-Pole 

 Trail, by Dr. Carter; the other,, represented in Fig. 14, Plate II, and Fig. 42, 

 Plate VI, was found at Grizzly Buttes, by Dr. Corson. 



In both specimens, which belonged to animals at maturity but not advanced 

 in life, the number of teeth in the molar series is six, or one less than in 

 Hyrachyus, and the same number as in Lophiodon and the tapir. The last 

 molar, however, has a bilobed crown as in the latter, but the premolars, in 



