_Eocene fauna of South America._--The few remains yet discovered in the Tertiary deposits of the Pampas which are believed to be of Eocene age, are exceedingly interesting, because they show us another change in the scenery of the great drama of life; there being apparently a considerable resemblance, at this epoch, between South America and Europe. They consist of a large extinct feline animal, _Eutemnodus_; of _Palæotherium_ and _Anoplotherium_, the well-known extinct Ungulates of the European Tertiaries, and which have never been found in North America; and of three genera of Rodents,--_Theridromys_, allied to _Echimys_, and found also in the Eocene and Miocene of France; _Megamys_, allied to the living _Capromys_ of the Antilles, and also to _Palæomys_, an extinct form of the French Miocene; and a very large animal referred to _Arvicola_, a genus found also in the Pliocene deposits of South America, and abundant in the northern hemisphere. No Edentates have been found. The resemblances of this fauna to that of Europe rather than to any part of America, are so strong, that they can hardly be accidental. We greatly want, however, more information on this point, as well as some corresponding evidences as to the condition of West and South Africa about the same epoch, before we can venture to speculate on their bearing as regards the early migrations of organic forms. _General Remarks on the Extinct Mammalian Fauna of the Old {149}and New Worlds._--Leaving the more special applications of palæontological evidence to be made after discussing the relations of the existing fauna of the several regions, we propose here to indicate briefly, some of the more general deductions from the evidence which has now been laid before our readers.