THE MAMMALIA OF THE UINTA FORMATION. 4G7 



lar, though less striking, ditiereiice exists between the Bridger and Washakie basins 

 with regard to the number and variety of the smaller forms. The great assemblage 

 of Icmuroids and pseudo-Icmuroids which the Wasatch and Bridger show so abun- 

 dantly is thus far represented in the Uinta only by the single species IJijoyi^odus 

 (iracilts Maish ; the Insectivora, Chiroptera, and Marsupialia have not been found at 

 all, though there is hardly room for doubt that they existed, inasmuch as they occur 

 both in the Bridger and the White River. Rodentia are also rare and only one form 

 can be certainly named, a species of Plesiarctomys, which genus is abundant in the 

 Wasatch, Wind River, and Biidger beds. A second species of rodent is apparently 

 implied by a lower incisor with a fragment of the mandible; it is, however, much 

 larger than any known rodent of the Bridger or White Kiver, and may possibly be- 

 long to some tillodont ; but this is not at all probable, as the tooth is much more 

 like that of a rodent, besides being smaller than that of any Bridger tillodont. We 

 have still therefore to search for the forerunners of the beavers, mice, and hares of 

 the White River. 



So far but a single creodont is certainly known to occur in the Uinta fauna, a 

 very large species of Mesonyx. This family ranges therefoi-e throughout the Eocene 

 of Nortii America, being represented by Dissacus in the Puerco, PacJujama in the 

 Wasatch and Mesonyx in the Bi'idgcr and Uinta. The absence of the upper molars 

 from the specimen before us precludes the possibility of a final reference of it to 

 Mesonyx ; but there can be no doubt that it is a member of the famil3^ A second 

 creodont is jjcrhaps indicated by a small lower sectorial molar and a premolar ; if so, 

 the animal must have belonged to the Miacidiv, or it may be a true carnivore. The 

 creodont nature of the specimen is the more probable on account of the greater like- 

 ness of the Uinta fauna to the Bridger. In any case this animal very probably rep- 

 resents the foreninner of the dog-like forms of the White River, the so-called AmpJii- 

 cyon and Galecynus. and possibly of Dinictis as well. Nothing is as yet known of 

 any Uinta forms which would serve to connect the hya^nodonts of the AVhite River 

 with the Oxycena and Protopsalis of the Bridger. 



The Perissodactyla of the Uinta are of great interest, as they are plainly inter- 

 mediate between those of the Bridger and those of the White River. The curious 

 family of Titanotheiidn' has its Uinta member in Diphicodon, which thus comiecls the 

 Bi idgei- genera I'ahi'osyops and Leurocrplndus with the I'itanollieriam (Moiodns) of 

 the White River. IIyr(idiynf>,Ho frequent in the Bridger, has apparently disajjpeared, 

 its place being taken by Tri]d(qms. which already occurs in the Washakie bed."?, 

 though sparsely. In the Uinta it is one of the nK)st abundant of all the lossils, and 

 is highly characteristic of the formation. Another genus, rare in tlir Washakie. 



