rally black or dark brown. The light colors of our miocene beds 

 are almost unknown, and the bones are always much harder than 

 these, or even than the fossils of the Bridger group of Wyoming. 

 These facts, in connection with the reduced number of exposures 

 of the beds, account for the comparatively small number of species 

 obtained, and the feeble representation of certain groups, e.g., the 

 birds, lizards, rodents, etc. Nevertheless a large number of in- 

 dividuals were obtained, and a considerable extent of country 

 explored, and I believe that the synopsis above given is an approxi- 

 mation to an expression of the characteristics of the most abund- 

 ant types, or, of the relative numerical representation in the fauna 

 of the different genera, orders, etc. 



Compai'ison with the established scale of geological horizons of 

 Europe has established the fact that the beds in question belong 

 to the Eocene category, as I have already shown 1 to be true of the 

 longer-known Bridger beds of Wyoming. It remains to collate 

 them with the numerous subdivisions of that period. The differ- 

 ences between the Wahsatch and Bridger fauna? have been in part 

 pointed out in my Report on the Vertebrate Fossils of New Mexico, 

 18Y4, 2 and may be more fully stated as follows: — 



1. Divisions found- in the Wahsatch beds not yet reported from 

 the Bridger beds. Aves, genus Diatryma (allied to Gastornis) ; 

 mammalia, Teeniodonta; Phenacodus ; Goryphodon ; 3 Meniscothe- 

 rium; most species of Hyracotherium. 



2. Divisions found in the Bridger beds not yet found in the 

 Wahsatch: fishes, Amiidse; reptiles, Ophidia; Anostira; mam- 

 mals, Mesonychiidse ; Tillodonta; Achsenodon; Dinocerata; Pa- 

 leeosyops; most species of Hyrachyus. 



The Wahsatch horizon of Wyoming has not yielded so many 

 species of vertebrata as those of New Mexico, but the close re- 

 semblance of the two faunae may be observed in the following list 

 of forms which I obtained at several localities : Fishes, Siluroids ; 

 mammals, Hyracotherium, two species; Phenacodus; Goryphodon, 

 two to three species. As is well known the Wahsatch beds under- 

 lie those of the Bridger group, and we therefore look for their 

 European equivalent in the lower part of the series. It has been 

 already pointed out 5 that the absence of Hyopotamus and Anoplo- 

 therium and allied genera, from the Bridger horizon precludes an 

 identification with the upper Eocene of Europe. The comparison 

 of the Wahsatch fauna with that of the lowest of the three divi- 

 sions into which Professor Gervais has arranged the European 



1 Proceedings American Philosophical Society, 1872, February and July. 



2 Annual Report of Chief of Engineers, p. 592. 



3 The species described by me as Batlimodon constitute a section of this 

 genus, characterized by the absence of tubercle or ridge between the inner 

 cusps of the last lower molar. I do not maintain this section as a distinct 

 genus. 



1 See Report of the U. S. Geol. Surv. Terrs., 4to. ii. p. 33-39. 

 5 Ann. Rept. U.S. Geol. Surv. Terrs., 1873 (1874). 



