The Peccaries (2 species), are peculiar to the Neotropical region, extending from Mexico to Paraguay. They also spread northwards into Texas, and as far as the Red River of Arkansas, thus just entering the Nearctic region; but with this exception swine are wholly absent from this region, forming an excellent feature by which to differentiate it from the Palæarctic. _Sus_ (14 species), ranges over the Palæarctic and Oriental regions and into the first Australian sub-region as far as New Guinea; but it is absent from the Ethiopian region, or barely enters it on the north-east. _Potamochoerus_ (3 species?), is wholly Ethiopian (Plate V. vol. i. p. 278). _Babirusa_ (1 species), is confined to two islands, Celebes and Bouru, in the first Australian sub-region. _Phacochoerus_ (2 species), ranges over tropical Africa from Abyssinia to Caffraria. Dr. J. E. Gray divides true swine (_Sus_) into 7 genera, but it seems far better to keep them as one. _Fossil Suidæ._--These are very numerous. Many extinct species of wild hog (_Sus_), are found in Europe and North India, ranging back from the Post-pliocene to the Upper Miocene formations. In the Miocene of Europe are numerous extinct genera, _Bothriodon_, _Anthracotherium_, _Palæochoerus_, _Hyotherium_, and some others; while in the Upper Eocene occur _Cebochoerus_, _Choeropotamus_, and _Acotherium_,--these early forms having more resemblance to the peccaries. None of these genera are found in America, where we have the living genus _Dicotyles_ in the Post-pliocene and Pliocene deposits, both of North and South America; with a number of extinct genera in the Miocene. The chief of these are, _Elotherium_, _Perchoerus_, _Leptochoerus_, and _Nanohyus_, all from Dakota, and _Thinohyus_, from Oregon. One extinct genus, _Platygonus_, closely allied to _Dicotyles_, is found in the Post-pliocene of Nebraska, {216}Oregon, and Arkansas. _Elotherium_ is said to be allied to the peccary and hippopotamus. _Hyopotamus_, from the Miocene of Dakota, is allied to _Anthracotherium_, and forms with it (according to Dr. Leidy) a distinct family of ancestral swine. It thus appears, that the swine were almost equally well represented in North America and Europe, during Miocene and Pliocene times, but by entirely distinct forms; and it is a remarkable fact that these hardy omnivorous animals, should, like the horses, have entirely died out in North America, except a few peccaries which have preserved themselves in the sub-tropical parts and in the southern continent, to which they are comparatively recent emigrants. We can hardly have a more convincing proof of the vast physical changes that have occurred in the North American continent during the Pliocene and Post-pliocene epochs, than the complete extinction of these, along with so many other remarkable types of Mammalia.