12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



Mile fauna described by McKenna is suggested by an upper molar 

 referred to primitive Hyopsodus loomisi, and by this together with 

 a lower molar of Pelycodus{ ?) praetutus and teeth of Meniscotherium, 

 cf . priscum, a resemblance to the Bitter Creek fauna is also seen. 



Bitter Creek. — Most significant of the newly worked localities is 

 a prominent hill of north- and westerly- facing exposures approxi- 

 mately a mile and a quarter south of Bitter Creek Station on the 

 Union Pacific Railroad in Sweetwater County. This is surely the 

 locality Cope (1872) referred to as Black Buttes in his description 

 of Coryphodon armatus. It is the nearest exposure of Wasatchian 

 materials to the Black Buttes station a few miles to the west, and the 

 topographic feature of that name is still more remote in the older 

 formations of the Rock Springs uplift. Marsh's parties also made 

 collections here in 1876 and 1882, including the specimens he described 

 as Eohippus pernix. The Marsh material, except for the hyracothere, 

 has not been previously described. The exposures at this locality are 

 on the west or northwest side of the Washakie Basin and may like- 

 wise be considered as on the east flank of the Rock Springs uplift. 

 The locality is in the lowest part of the Knight, but little above the 

 Paleocene. The contact or transition between these sets of beds is 

 obscured locally by the alluvium of Bitter Creek. Fossils were en- 

 countered in various lithologic zones, including the thicker sandy 

 marls, where more than one good skull of Coryphodon was obtained, 

 but many of the smaller jaws and teeth were found in or adjacent to 

 the thin carbonaceous layers which abound In spines and other frag- 

 ments of fish. 



A fauna of about 24 species of mammals representing 21 genera 

 was recognized in the combined National Museum and Yale University 

 collections. The fauna closely resembles that of the Gray Bull beds 

 in the Bighorn Basin, and the small condylarths Haplomylus speirianus 

 and Meniscotherium, cf. priscum, suggest correlation with the earlier 

 part of Gray Bull series. The genera here are nearly all included in 

 the larger Four Mile fauna and differences in certain of the species 

 represented may in part reflect local conditions or environment. Most 

 noticeable with regard to the Four Mile fauna is the absence of 

 Meniscotherium, which so far has not been found in any of the 

 horizons on the east side of the Washakie Basin. This must surely 

 represent a persistent ecological difference. 



Four Mile Creek. — To the southeast of the Washakie Basin in the 

 adjacent part of Colorado, but nevertheless within the more general 

 area of the Washakie basin of deposition, a number of localities in 



