CHAP. VII.] 
MAMMALIA OF THE NEW WORLD. 
137 
recently discovered, forming tbe 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 Accrathcrium. They were 
of rather small size. 
Next to these extinct rhinoceroses come the Brontotheridm, 
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, Brontotkerium, 
Titanotherium , Megacerops, 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, Symborodon, 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, 
( Dicotyles ) 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. 
From the Miocene are three allied genera, Nanohyus , Lepto- 
chcerus, and Perchcerus. Professor Cope, however, thinks Lepto- 
ckcerus may be Lemuroid, and allied to Menotherium. The 
Anthracotheridee, a family which connects the Hippopotamidm 
and Euminants, 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 
