chap, vii.] MAMMALIA OF THE NEW WORLD. 137 



recently discovered, forming the genus Diccratherium. 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 Brontotheridse, 

 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, 

 Titanotherium, Mcgaccrops, and Anisacodon, distinguished by 

 peculiarities of dentition. Though most nearly allied to the 

 rhinoceroses, they show some affinity for the gigantic Dino- 

 cerata of the Eocene to be noticed further on. Professor Cope 

 has since described another genus, Symhorodon, from the Mio- 

 cene 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. 



We commence the Artiodactyla, or even-toed Ungulates, with 

 the hog tribe. These are represented by species of peccaries, 

 (Dicotylcs) from the Pliocene of Nebraska and Oregon ; and by 

 an allied form Thinohyus, very like Dicotyles, but having an 

 additional premolar tooth and a much smaller brain-cavity. 

 Prom the Miocene are three allied genera, Nanohyus, Lepto- 

 chcerus, and Perchcerus. Professor Cope, however, thinks Lepto- 

 chcerus may be Lemuroid, and allied to Menotherium. The 

 Anthracotherida?, a family which connects the Hippopotamidre 

 and Ruminants, and which occurs in the Miocene of Europe 

 and India, are represented in America by the genus Hyopotamus 

 from the Miocene of Dakota, and Elotherium from the Miocene of 

 Oregon and the Eocene of Wyoming; the latter genus being some- 

 times classed with the preceding family, and lately placed by 

 Professor Marsh, in the new order, Tillodontia. Professor Cope 

 has since described three other genera from the Eocene of New 



Vol. L— 11 



