1887.] ^OrS [Sco^t and Osborn. 



slve bearing upon the cuboid, while it is narrower than in Menodns, and 

 has a less extensive contact with the cuboid. Tlie number of digits is 

 apparently iv-iii. 



The characters revealed by this skeleton abundantly confirm Professor 

 Marsh's view that Diplacodoti is to be regarded as the ancestor of 3/e«odws, 

 and as a descendant of the Bridger Chalicotherioids. 



The Uinta fauna differs in many very important respects from that of 

 the Bridger formation, both in what it possesses and in what it lacks ; nev- 

 ertheless it is on the whole more closely akin to the Bridger than to the 

 White River fauna. The great Dinocerata seem to have completely dis- 

 appeared, as have also the Tillodonta ; rodents, lemiiroids, and creodonts 

 are very much less common than in the Bridger, and what seem to be the 

 first true American carnivores have appeared ; perissodactyls of chali- 

 cotherioid, lophiodont, equine and rhinocerotic types are still very numer- 

 ous. But the most remarkable and striking change consists in the extra- 

 ordinary increase in the number of selenodont artiodactyls, which are 

 exceedingly rare in tlie Bridger, but in the Uinta are perhaps more abun- 

 dantly represented, as far as individuals are concerned, than any other 

 group of mammals ; in character these artiodactyls are distinctly like 

 those of the White River epoch. As yet no bunodont artiodactyls haA'^e 

 been discovered, though they doubtless existed. With the possible excep- 

 tion of Agriochoerus (see p. 257), no genus is yet known which is com- 

 mon to the White River and Uinta formations, while several Bridger 

 genera are represented in the latter ; there are Plesiarctomys, Mesonyx, 

 Ilyrachyus, Amynodon, and perhaps others. No perissodactyl in which 

 the premolars have all taken on the molar pattern, and no artiodactyl 

 with coalesced metapodials, is known in this fauna, which thus has a dis- 

 tinctly older facies than the fauna of Quercy,* which, hop,'ever, agrees 

 witli it in the great increase in selenodonts. Schlosserf considers the Uinta 

 fauna as Oligocene, but, as we believe, without good reason, since not a 

 single Miocene genus has been found in it, the genera being all either com- 

 mon to the Bridger or peculiar to the Uinta. The term oligocene is much 

 more properly applied to the overlying White River beds, as has been 

 done by Messrs. Cope and Filliol.:]; It seems, therefore, best on the whole 

 to regard the Uinta as forming the summit of the eocene, as Professor 

 Marsh, who first described its fauna, has done. 



Synopsis of the Uinta Fauna. 



Genera. Species. 



Rodentia 3 2 



Lemur oidea 1 1 



Creodonta 1 1 



* Filhol Phosph. du Quercy, pp. 517-554. 



t Morph. Jahrb., Bd. xii, p. 



X Bibl. de I'Ecole d. Hautes Etudes ; Sect. d. Sci. Nat. T., xix, p. 21 (separatim). 



