NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 73 



length than in P*. In these the primary cusp and tritocone (paracone 

 and metacone) are less widely separated than in P*, or than in P^ 

 of later forms. In each the protoloph extending toward the parastyle 

 is not appreciably deflected anterolingually, but shows a distinct en- 

 largement representing the protoconule, certainly more discernable 

 than in the specimen figured by Kitts (1956, fig. 5) for this species. 

 All these, moreover, are of a size commensurate with the smaller La 

 Barge specimens earlier referred to H. index. I suspect that there 

 is a considerable amount of variation in the development and posi- 

 tion of the protoconule of P^ in any population of Hyracotherium and 

 I have attempted to illustrate this in plate 13 where the specimens 

 in figures 4 to 9 inclusive show increasing significance of the proto- 

 conule in the La Barge material of i^. vasacciense. 



It seems more than likely that the comparatively advanced lower 

 Knight form represented at Bitter Creek gave rise to typical H. 

 vasacciense of the later Knight beds, possibly in a dichotomous ar- 

 rangement, such as seems indicated in the La Barge materials (see 

 Kitts, 1956, p. 49; and Gazin, 1952, p. 65) other than those now 

 referred to H. craspedotum. 



Marsh's type of Eohippus pernix is from the Bitter Creek locality. 

 This name was regarded by Kitts as a synonym of Hyracotherium 

 vasacciense. It is possible that this interpretation is correct, but it 

 seems more than likely, in the absence of published information to the 

 contrary, that he regarded the Bitter Creek fauna as later than it is. 



A few isolated teeth from the Red Desert locality and about 24 

 specimens from the Lower Wasatchian or Gray Bull level to the west 

 of Elk Mountain in Fossil Basin are also referred tentatively to H. 

 angustidens. The latter show a range in size as great as that at Bitter 

 Creek but with a somewhat greater average size. A single maxillary 

 portion exhibits P^ and P* (pi. 13, fig. 3) and these teeth more nearly 

 approximate the nonmolariform condition cited by Kitts for this 

 species. 



HYRACOTHERIUM VASACCIENSE (Cope) 



Plate 13, figures i, 2, 4-10) 



As revised by Kitts, Hyracotherium vasacciense includes among its 

 synonyms Hyracotherium index, the second and smaller of the two 

 species described by Cope from the Knight beds of Fossil Basin. 

 Although I have shown that for the La Barge collection M2, excluding 

 the very large specimens, is clearly bimodal in its proportions, and 

 Kitts (1956, p. 52) has found the same to be true for M3, the evidence 



