THK MAMMALIA OF THE UINTA FOUMATION. 405 



western basin, especially of the smaller mammals, the crciodonts, lemiiroids and insec- 

 tivores, which are comparatively rare in the AVashakie and very abnndant in the 

 Bridgcr. No tillodonts have yet been reported from the former. The perissodac- 

 tyls are quite diifcrent. l*al<eos;/ops is somewhat less abundant in individuals in the 

 eastern basin, but /*. major and palndosus are both present, and there are in the 

 Princeton Museum two undescribed species of this genus from the AVashakie which 

 differ markedly from any yet found in the Bridger, and one of them, l)y its great size, 

 seems to approximate closely Diplacodon. Hyrachyus is represented by the same or 

 similar species and in about equal numbers in both areas. On the other hand the 

 Uinta rhinoceros Aovjnodon (== Orthocynodon nobis) is found only in the eastern 

 i-egion, and the same is almdst certainly true of Triplopus, while Colonoceras occurs 

 only in the Bridger basin. Among the artiodactyls the chief diiterence is to be 

 Ibund in the presence and frequency in the eastern basin of the large species of 

 Achvnodon, A. insolens and ^1. rohistiis. JTeloIiyus and Ilomacodon have not yet 

 been reported from this region, but as representatives of these series occur in the 

 Uinta, we may confidently expect that they will be found in the AVashakie. 



Another strikiny; difference between the two basins is to be found in the fades 

 of the Dinocerata so common everywhere. The great variability of these animals 

 precludes the making of any very sharp distinctions between those of the two ai-eas, 

 but in a general way and with some exceptions they are in rather strong contrast 

 with each other. The prevailing type of skull in the Bridger basin is comi)aratively 

 short and broad, the nasal tuberosities are of moderate size, the parietal protuberances 

 are placed well forward, and the parieto-occipital crest is of moderate height. The 

 Washakie forms have generally a long narrow skull, with very large nasal tuberosi- 

 ties, the j)arietal protubei-ances are placed far back, the parieto-occii)ital crest is very 

 high ; the cervical vertebraj in these species are also as a rule shorter than in those 

 of the Bridger area, and the animals tend to become of a larger size. 



Making all due allowance for sources of error, it is difficult to believe that these 

 differences are to be explained by geographical considerations, while on the other 

 hand the strati graphical relations of the AVashakie beds to the underlying Green 

 Kiver scries present objections to the assumption that the latter could have been a 

 land surface for any great length of time. But these relations ai'c by no means clear 

 and very much need to l»e re-examined. 



AV'e have no information relative to the small area east of Vcrtniliou cn-ok. but 

 in all j)robability it is simply an outlier of the AVashakic. 



From pi-esent knowledge, we are therefore justilied in making a tlirciliiM sub- 

 division (>r liu- Bi idger epoch, willi ilic Wind liiver licds at llic l>;t<c and the 



