NO. 8 UPPER EOCENE ARTIODACTYLA — GAZIN 3 1 



tion with respect to Simimeryx and Hypertragulus. This has been 

 considered by Stock (1934) and is further discussed in the portion 

 of this paper treating with the hypertraguHds. The possible ancestry 

 of Mesomeryx may Hkely be in a middle Eocene homacodont rather 

 like Homacodon, but having a reduced or no hypocone on the upper 

 molars. Mesomeryx is rather like Microsus, but here again the differ- 

 ence lies in the absence of a hypocone. 



MESOMERYX GRANGERI9 Peterson, 1919 



Type.—Leh maxilla with P^ to M^, inclusive, CM. No. 3189. 



Horizon and locality. — The horizon and locality are given as Uinta, 

 lower C, 2 miles east of Dragon- Vernal stage road, Uinta Basin, Utah, 

 by Peterson (1919, p. 73); however, the specimen label gives the 

 information "Uinta B" and "N. E. of Well No. 2." It was collected 

 by Douglass in 1908. 



Discussion. — Mesomeryx grangeri is much the smallest of the 

 upper Eocene artiodactyls, and almost as small as the middle Eocene 

 Microsus cuspidatus. Other characters of specific importance cannot 

 be determined as there is but one species known. 



MEASUREMENTS IN MrLLIMETERS OF DENTITION IN TYPE SPECIMEN OF 



Mesomeryx grangeri, cm. no. 3189 



P', anteroposterior diameter : transverse diameter* 44 : 3-3 



P*, anteroposterior diameter : transverse diameter 3.4 : 4.7 



M*, anteroposterior diameter : transverse diameter* 4.6 : 5.4 



M*, anteroposterior diameter : transverse diameter 4.8 : 6.5 



• Measurements of posterior upper premolars are taken anteroposteriorly across outer por- 

 tion and transversely perpendicular to outer margin. Those of upper molars are taken 

 anteroposteriorly perpendicular to anterior margin and transversely across anterior portion 

 of tooth. 



Genus PENTACEMYLUS Peterson, 1931 



Type. — Pentacemylus progressus Peterson. 



Discussion. — Pentacemylus is clearly related to Bunomeryx but 

 distinctly more progressive. It is different than the earlier Buno- 

 meryx, principally in exhibiting noticeably more crescentic cusps on 

 the upper molars and in the loss of the hypocone on M^. Bunomeryx 

 has a well-developed hypocone on M^ and a vestige on M^, whereas 

 Pentacemylus may have only a slight vestige of this cusp on the 

 cingulum of M^ and no evidence of it on M^. The upper premolars 

 appear to be only slightly more crescentic than in Bunomeryx, as 

 noted principally in the deuterocones. 



® Illustrated in Peterson, 1919, pi. 36, fig. 17. 



