NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 6l 



closer to V. asius, geographically as well as in form, so that it seems 

 preferable to regard them as a progressive mutant of F. asius. Their 

 stratigraphic position, of course, precludes regarding them in an 

 ancestral relationship to V. cmmvus. 



Cf. VULPAVUS, sp. 

 (Plate 8, figure 4) 



A right maxillary fragment with M^ and MS U.S.N. M. No. 22473, 

 from Bitter Creek closely resembles in the form of the two molar 

 teeth a specimen of Vulpaviis aiistralis (A.M. No. 16954) from the 

 Bighorn Basin but is distinctly smaller, and the inner cingulum, though 

 worn, appears a litde weaker. Matthew did not discuss or figure upper 

 teeth of Vulpavus but it would appear from these teeth that there is 

 somewhat less disparity in size between M^ and M^ and possibly the 

 external shelf like cingulum is not as expanded as in Miacis. 



VASSACYON, cf. PROMICRODON (Wortman) 



A portion of the left ramus of a mandible, U.S.N. M. No. 22451, 

 from the Gray Bull horizons southwest of Elk Mountain in the 

 Fossil Basin represents beyond doubt, Matthew's genus Vassacyon. 

 Only P4 and the talonid portion of the lower carnassial are included, 

 but these together with alveoli for other molars correspond closely 

 in size to Gray Bull V. promicrodon. The distinguishing feature in 

 this specimen, demonstrating that it represents Vassacyon, is seen 

 in the molar talonid. The heel of Mi, though having a well-defined 

 lingual basin, has a comparatively high median crest. The basin is 

 not as large and broad as in Miacis or Vulpavus and the crest is more 

 trenchant. The median crest suggests Uintacyon, but this is denied 

 by the much better-defined basin. Moreover, the jaw is relatively deep 

 and robust as in Vassacyon promicrodon. 



CONDYLARTHRA 



HYOPSODONTIDAE 



HAPLOMYLUS SPEIRIANUS (Cope) 



(Plate 9, figures 1-4) 



Haplomylus speirianus, as pointed out by Matthew (1915b, p. 314)* 

 is characteristic of the lower part of the Gray Bull and has not been 

 found in the upper Gray Bull, Lysite, or Lost Cabin beds. This species 

 is now recognized in the materials from several localities in the lower 

 part of the Knight sequence. In addition to isolated upper and lower 



