The geographical distribution of animals, with a study of the relations ...

chap, vii.] MAMMALIA OF THE NEW WORLD. 137recently discovered, forming the genus Diccratherium.These hada pair of nasal horns placed side by side on the snout, not behindeach other as in existing two-horned rhinoceroses, the rest oftheir skeleton resembling the hornless Aceratherium. They wereof rather small size.Next to these extinct rhinoceroses come the Brontotheridse,an extraordinary family of large mammalia, some of whichexceeded in bulk the largest living rhinoceros. They had fourtoes to the front and three to the hindfeet, with a pair of largedivergent horns on the front of the head, in both sexes. ProfessorMarsh and Dr. Leidy have described four genera, Brontotherium,Titanotherium, Megacerops, and Anisacodon, distinguished bypeculiarities of dentition. Though most nearly allied to therhinoceroses, they show some affinity for the gigantic Dinocerataof the Eocene to be noticed further on. Professor Copehas since described another genus, Symborodon, from the Mioceneof Colorado, with no less than seven species, one nearlythe size of an elephant. He thinks they had a short tapir-likeproboscis. The species differ greatly in the form of the craniumand development of the horn -bearing processes.We commence the Artiodactyla, or even-toed Ungulates, withthe hog tribe. These are represented by species of peccaries,{Dicotyles) from the Pliocene of Nebraska and Oregon ; and byan allied form Thinolujus, very like Dicotyles, but having anadditional premolar tooth and a much smaller brain-cavity.From the Miocene are three allied genera, Nanohyus, Leptochcerus,and Perchce-rus. Professor Cope, however, thinks Leptochcerusmay be Lemuroid, and allied to Menotherium. TheAnthracotheridae, a family which connects the Hippopotamidseand Euminants, and which occurs in the Miocene of Europeand India, are represented in America by the genus Hyopotamusfrom the Miocene of Dakota, and Elotherium from the Miocene ofOregon and the Eocene of Wyoming; the latter genus being sometimesclassed with the preceding family, and lately placed byProfessor Marsh, in the new order, Tillodontia. Professor Copehas since described three other genera from the Eocene ofVol. L—11New