NO. I LOWER EOCENE MAMMALIAN FAUNAS GAZIN 67 



osbornianum, but evidently does not represent this genus. The cusps 

 are lower and more bunodont and there is much less indication of 

 transverse lophs. Moreover, the enamel is perhaps a little more ru- 

 gose. Although the more characteristic P4 of Phenacodus brachypter- 

 nu>s is not included in the material, it seems probable, nevertheless, that 

 this small species is represented rather than somewhat larger P. vort- 

 mani or P. copei. 



MENISCOTHERIIDAE 



MENISCOTHERIUM, cf. PRISCUM Granger 



(Plate 10, figures 5 and 6) 



A small species of M eniscotherium in the Bitter Creek fauna is 

 represented by about six specimens. Although the type of M. prisciim 

 from the Clark Fork beds could not be located in the American 

 Museum collections, the dimensions of the teeth given by Granger 

 (1915, p. 360) are closely comparable to those in the Bitter Creek 

 specimens. Their size is only slightly greater than in the New Mexican 

 form M. tapiacitis Cope, but, as noted by Granger, the metastylid of 

 the lower molars is much more prominent in the Wyoming material. 



In a comparison of upper cheek teeth in a maxilla from Bitter 

 Creek (see pi. 10, fig. 5) with upper dentitions from later horizons of 

 the Wasatch, it is noted that in addition to smaller size the teeth are 

 relatively short (anteroposteriorly) and broad. The extended lingual 

 portion in each also seems anteroposteriorly compressed. 



Isolated teeth of distinctly small size from the Red Desert locality 

 are also referred to this species. Moreover, fossil materials collected 

 by Henry W. Roehler near the base of the Knight sequence at locali- 

 ties on the western and southeastern flanks of the Rock Springs uplift 

 include isolated teeth of this species in association with Haplomylus 

 speirianus. The faunal levels represented are about comparable to 

 those at Bitter Creek. 



Some very fragmentary material, but including one complete lower 

 molar, of a small M eniscotherium was found low on the south-facing 

 escarpment to the west of the saddle north of Fossil Butte. The 

 tooth is almost identical in size with M2 in the lower jaw (U.S.N.M. 

 No. 22432 ; pi. 10, fig. 6) from Bitter Creek. The presence of 

 M eniscotherium so close in size to M. priscum on the slopes on the 

 opposite side of the ravine to the northwest of Fossil Butte is rather 

 indicative of a lower Gray Bull level in this area, lower than the 

 Wasatchian horizon represented in the saddle which has produced 

 remains of M eniscotherium more nearly comparable to M. rohustum. 



