Allied to these, are a series of forms showing a transition to the tapirs, and to the _Palæotherium_ of the European Eocene. In the Pliocene we have _Parahippus_; in the Miocene _Lophiodon_, found in the same formation and in the Eocene of Europe, and allied to the tapir; and in the Eocene, _Palæosyops_, as large as a rhinoceros, which had large canines and was allied to the tapir and _Palæotherium_; _Limnohyus_, forming the type of a family Limnohyidæ, which included the last genus and some others mentioned further on; and _Hyrachyus_, allied to _Lophiodon_, and to _Hyracodon_ an extinct form of rhinoceros. Besides these we have _Lophiotherium_ (also from the Eocene of Europe); _Diplacodon_ allied to _Limnohyus_, but with affinities to modern Perissodactyla and nearly as large as a rhinoceros; and _Colonoceras_, also belonging to the Limnohyidæ, an animal which was the size of a sheep, and had divergent protuberances or horns on its nose. A remarkable genus, _Bathmodon_, lately described by Professor Cope, and of which five species have been found in the Eocene of New Mexico and Wyoming, is believed to form the type of a new family, having some affinity to _Palæosyops_ and to the extinct Brontotheridæ. It had large canine tusks but no horns. The Rhinocerotidæ are represented in America by the genus _Rhinoceros_ in the Pliocene and Miocene, and by _Aceratherium_ and _Hyracodon_ in the Miocene. Both the latter were hornless, and _Hyracodon_ was allied to the Eocene _Hyrachyus_, one of the Lophiodontidæ. In the Eocene and Miocene deposits of Utah, and Oregon, several remarkable extinct rhinoceroses have been {137}recently discovered, forming the genus _Diceratherium_. These had a pair of nasal horns placed side by side on the snout, not behind each other as in existing two-horned rhinoceroses, the rest of their skeleton resembling the hornless _Aceratherium_. They were of rather small size. Next to these extinct rhinoceroses come the Brontotheridæ, an extraordinary family of large mammalia, some of which exceeded in bulk the largest living rhinoceros. They had four toes to the front and three to the hind feet, with a pair of large divergent horns on the front of the head, in both sexes. Professor Marsh and Dr. Leidy have described four genera, _Brontotherium_, _Titanotheium_, _Megacerops_, and _Anisacodon_, distinguished by peculiarities of dentition. Though most nearly allied to the rhinoceroses, they show some affinity for the gigantic Dinocerata of the Eocene to be noticed further on. Professor Cope has since described another genus, _Symborodon_, from the Miocene of Colorado, with no less than seven species, one nearly the size of an elephant. He thinks they had a short tapir-like proboscis. The species differ greatly in the form of the cranium and development of the horn-bearing processes.