Vol. 6] 



Merriam: Virgin Valley and, Thousand Creek. 



259 



exactly the same size, according to the figure, as that of an un- 

 named species of Hypohippus described by Gidley 1 ' 1 from the 

 Loup Fork of South Dakota. 



The permanent inferior cheek-tooth dentition of a species of 

 Hypohippus apparently identical with the form described by 

 Gidley is exhibited in several specimens. A lower jaw (no. 12587, 

 figs. 28a and 285) shows all of the lower molars and premolars 

 perfectly preserved excepting a small portion of M 3 and P v A 

 series of three perfectly preserved teeth (no. 11760, figs. 26 and 

 27), found together, represent molars one to three of another 

 individual. 



In general the teeth of specimen 12587 resemble the inferior 

 series of H. equinus as figured and described by Scott. They 

 differ in their relatively greater width and in the smaller size of 

 P 1 . The posterior region of the median internal, or metaconid, 

 pillars is not distinctly angular as in H. equinus as figured by 

 Scott. This difference may be due in part to wear. On P 3) P 4 , 

 and M x a very small tubercle appears on the inner side between 

 the metaconid and entoconid. In Mj and M 2 there is no sugges- 

 tion of a groove separating a metastylid from the metaconid. 

 There is in fact no distinct metastylid present. The external 

 cingulum is quite strongly developed. 



The three molars comprising no. 11760 show apparently the 

 same dimensions as no. 12587. The posterior region of the meta- 

 conid is distinctly angular as in II. equinus, the hypostylid is a 

 little more prominent than in no. 12587 and the small tubercle is 

 not present between the inner borders of the metaconid and 

 entoconid. Though distinguished by the slight difference just 

 mentioned it is hardly probable that these two forms are specifi- 

 cally separable. 



A well preserved upper molar one or two (no. 11570, fig. 25) 

 represents a form of Hypohippus in which the teeth appear to be 

 relatively somewhat narrower anteroposteriorly than in II. 

 equinus, and in this respect approach the type of H. osbomi. 



An upper molar specimen (no. 12564, fig. 24) is apparently 

 identical in size with M 3 of H. osbomi. The abruptness of the 



is Gidley, J. W., Bull. Amer. Mus. Nat. Hist., vol. 22, p. 136, 1906. 



