M.U COPE ON HOEIZONS OF EXTINCT VEETEBRATA. 45 



below the Aquitanian in Europe. But the American BideljyJiys, * Hyce- 

 nodo7i, Aonphicyoji, JElotheriimi, and Hyopotamus^ with the numerous 

 Chalicotheroicl species, show clearly that the White Eiver fauna may be 

 looked upon as a mixture of those of the Stampian and Aquitanian, the 

 former of which is sometimes referred with reason to the Ui)per Eocene, 

 while the latter is always left in the lowest Miocene. And the solution of 

 this question of position as regards the White Eiver beds appears to me 

 to be at present by no means easy, t According to the system of E"au- 

 mann, it should be called Oligocene. 



Although Artiodactyles with Selenodont molars are far more abundant 

 in both continents during this period than the last, a remarkable differ- 

 ence is to be observed between them. Those of Europe still largely 

 consist of the types with five crescents, as represented by the numerous 

 Hyopotami and Ccenotheria, while in America the modern four-crescent- 

 bearing molar characterizes almost the entire suborder, the only excep- 

 tion being two species of Hyopotmmis. 



The following table will represent the relations of the White Eiver 

 fauna: 



Stampian and Aquitanian. White Eiyer. 



Didelphys. Didelphys. 



Leptictidce. 

 ProtomyidcB. Frotomyidce.X 



SacGomyidcB.^ 

 Steneofiher. Steneofiher. 



LeporidcB. Leporidce. 



Hycenodon. Hycenodon. 



AmpMcyon. Amphicyon. 



Canis. Canis. 



Temnocyon. 



Bnhydrocyon. 

 Gulo.\\ Gulo.\\ 



Dinictis. 

 Maclicerodus. Machcerodus. 



Chalicotheriidce. 



Palceotheriidce. 



JSyracodon. 



Acerathernim. 



AncMtlierium. 

 Elotlierium. Elotherium. 



Palwochoenis. Palwochcerus. 



* Eerpetothermm Coj)e ; Peratherium Aym. 



t See Aun. Report U. S. Geol. Siirr. Terra. 1873, p. 462, where the White River beds 

 are determined as Lower Miocene. 

 t Ischyromys Leidy. 

 § Entoptychus and Pleurolicus Cope. 

 WAnij^hictis Pom. 



