1903.] Matthew, Fauna of Titanotheriiim Beds of Montana. 20T 



later horizon, while there is but one Uinta genus (Leptotrag- 

 ulus) and that represented by a rather divergent species. 

 This contrast is partly explained by the fact that the known 

 White River fauna is a very large one, while that from the 

 Uinta is comparatively small; partly also by considerations 

 of geographical distribution of the Oligocene mammals and 

 by different conditions of deposition in the Uinta and White 

 River beds. But, making allowance for all these, there seems 

 still to be a considerable gap between the Diplacodon and 

 Titanotherium faunas, while the latter is much closer to the 

 Oreodon fauna. It shows some marked differences, however: 

 (i) There are two new insectivore genera of the primitive 

 section (Zalambdodonta) of the order, which has hitherto 

 been practically unknown in a fossil state, unless the Eocene 

 species reported by Professor Marsh shall prove to belong to it. 



(2) All the rodents are sciuromorphs '^ or lagomorphs. 

 Myomorpha, more abundant than sciuromorpha in the Oreo- 

 don Beds, have not yet appeared. They are unknown in the 

 Eocene, except ProtoptycJms, a form of doubtful affinities. 



(3) The only Creodont from the Oreodon Beds is the highly 

 specialized HycBiiodon. At Pipestone Creek we have a more 

 primitive type, intermediate between Hycenodon and Sinopa. 

 At Swift Current Creek occurs Hemipsalodon {?z=Pterodon), 

 also less specialized than HycsJiodon. {HycBJiodon itself occurs 

 also in the Titanotherium Beds.) 



(4) Oreodon is not found, and two or three more primitive 

 genera (Bathygenys, Limnenetes, ? A griochcerus) ta.ke its place. 



(5) Hypertragulus, common in the Middle and Upper Oligo- 

 cene, is not foun.d, while Leptomeryx of the Lower and Middle 

 Oligocene is abundant and large. 



(6) In place of Poebrotherium, the camel of the Oreodon 

 Beds, is found a brachyodont form, apparently the Eocene 

 genus Leptotragulus . 



From the above facts we would infer that the Pipestone 

 Beds are at the base of the Oligocene, but above the Eocene, 

 accepting Osborn's correlation of the White River formation 



' If Gymnoptychus be considered a sciuromorph, as it was by Professor Cope and is 

 by Dr. Hay. 



