68 



ihcir less degree of (Icvelopinent in comparison wilh the molars, are more 

 like those of Lophiodon. 



The suppression of an anterior premolar may jierhaps he regarded as a less 

 important generic character than the others which have been indicated as 

 separating Hyrachyus from Lophiodon and Tapirus. Under the circum- 

 stances, notwithstanding the reduction in the number of premolars, I view 

 the two jaw-specimens above indicated as pertaining to Hyrachyus. 



Professor Marsh has described several specimens, from Grizzly Buttes, 

 under the name of hopModon nanus, which I suspect to belong to the same 

 animal as the lower-jaw fragments above indicated. Pie observes that the 

 most characteristic of the specimens is a right upper jaw containing a series 

 of four premolars and three molars. If, then, this really, belongs to the same 

 animal, it would give with the lower-jaw specimens, as the formula of the 

 molar series, seven teeth above and six below, as in the tapir. The upper 

 ]u-cmolars, however, jiresent a greater amount of difference from the molars 

 than in the latter, the difference being mainly diic to a less degree of develop- 

 ment of the premolars and in the connation of the inner lobes of their 

 crowns. 



The molar teeth and the portion of the jaw containing them are almost repe- 

 titions of form of the corresponding parts in Hyrachyus agrarius. The men- 

 tal foramen is situated below the first premolar. Hyrachyus nanus was 

 about half the size of //. agrarius. 



Measurements from two lower-jaw specimens areas follows: 



Space occupied by the complete series of molar teeth 2 .inches. 



Space occupied by the premolars 93 lines. 



Space occupied by the molars 14 lines. 



Depth of jaw below last premolar 10 lines. 



Diameter of llrst premolar 



Diameter of second premolar. 



Diameter of last premolar 



Diameter of fir.st molar 



Diameter of second molar . . . . 

 Diameter of last molar. 



Fig. 11, Plate XXVI, represents the greater part of the right ramus of 

 the lower jaw of Hyrachyus nanus, which I found, together with a fra'^mcnt 



