142 DISTRIBUTION OF EXTINCT ANIMALS. [paut ii. 



the American Pliocene and IMiocene periods, abounding in 

 genera and species ; whereas in Enrope the group only exists in 

 the Post-Pliocene or Lower Pliocene, with one Upper Miocene 

 species of Camclus in N. India. The Antliracotherida^ (extinct), 

 found only in the Upper Miocene of France and India, reach 

 even the Lower Eocene in America. 



These facts may be due, in part, to a want of strict co-ordina- 

 tion between the Tertiary deposits of Europe and North America, 

 — in part to the imperfection of the record in the latter country. 

 Yet it does not seem probable that they are altogether due to 

 these causes, because the Miocene beds, which are by far the 

 best known in America as in Europe, exhibit deficiencies of the 

 same kind as the less known Eocene deposits. The fossil fauna 

 of both countries is so rich, that we can hardly impute great and 

 well marked differences to imperfect knowledge ; yet we find 

 such important families as the Civets, Hyaenas, Giraffes, and 

 Hippopotami absent from America, with the Weasels, and Ante- 

 lopes almost so ; while America possesses almost all the Camelidae, 

 two peculiar orders, Dinocerata and Tillodontia, and four remark- 

 ably peculiar families, Limnotheridse, Lemuravidse, Oreodontidae 

 and Brontotheridae. If then the facts at present known represent 

 approximately the real time-relations of the groups in question 

 on the two continents, they render it probable that weasels, bears, 

 true horses, swine, oxen, sheep and antelopes, originated on the 

 Old World continent, and were transmitted to America during 

 some part of the Miocene period ; while camels originated in the 

 New World, and somewhere about the same time passed over to 

 Europe. Of the extinct families common to the two hemi- 

 spheres, the Anthracotheridae alone seem to have had an 

 American origin. Of the genera common to the two countries, 

 almost all seem to have had a European origin, the only genera 

 of equal date being the two rhinoceroses and three Anclii- 

 theridae ; but if the Brontotheridae are allied to the PJiinocerotidae, 

 these latter may have originated in America, although now an 

 exclusively Old World type. These conclusions are not im- 

 probable when we consider the much greater size of the Old 

 World continents, extending far into the tropics and probably 



