Though the number of artiodactyl families yet identified among the White River fossils is no larger than that of the perissodactyl families, the artiodactyls greatly preponderated in individual abundance. The peccaries, which were fairly common, resembled those of the John Day, but were considerably smaller. Of the camels, there were two series, one of which (_†Eotylopus_), lately described by Dr. Matthew, is of yet unknown significance, while the other (_†Poëbrotherium_) was apparently the ancestor common to all the subsequent phyla of camels and llamas. This extremely interesting genus had species which ranged in size from a gazelle to a sheep, had two toes in each foot, a moderately elongate neck and teeth which were beginning to assume the high-crowned character. From this it may be inferred that those animals were, partly at least, of grazing habit, which was rare among White River ungulates, most of which fed upon leaves and soft and succulent plants. An extinct family, the †Hypertragulidæ, were a greatly diversified group of dainty little creatures, one of which (_†Hypisodus_) was no larger than a rabbit and had high-crowned teeth. The other genera (_†Leptomeryx_, _†Hypertragulus_) must have resembled in form and proportions the tiny little chevrotains or “mouse-deer” of the East Indian islands. Late in the age arose a larger form of this family, nearly equalling the Musk-Deer in size, the extraordinary genus _†Protoceras_, which was, especially the males, a grotesque object. The males had a pair of upper canine tusks and two pairs of prominent long protuberances on the skull. This, or some similar form, must have been the ancestor of the still more bizarre _†Syndyoceras_ of the lower Miocene. The †oreodonts were by far the commonest of White River mammals, and evidently they roamed the woods and plains in great herds. There were several species, larger and smaller, of the abundant genus (_†Merycoidodon_) but the largest did not surpass a modern peccary in size and was somewhat like that animal in appearance, but had a shorter head and much longer tail. In the upper substage appeared a very peculiar genus of this family (_†Leptauchenia_), animals with short, deep, almost monkey-like heads, and presumably aquatic in habits. The _†agriochœrids_ were very much less common; they may be described roughly as †oreodonts with very long, cat-like tails and clawed feet. [Illustration: FIG. 136.—_†Merycoidodon culbertsoni_, the most abundant of White River †oreodonts. Restored from a skeleton in the American Museum of Natural History.]