The camels of the upper Oligocene (John Day) are still incompletely known, but appear all to have belonged to the series of grazers which led up to the modern genera. Future discovery may bring to light in the John Day earlier members of the †giraffe-camel series, of which a possible member is found in the uppermost substage of the White River, or perhaps both phyla united in the upper Oligocene, a question which remains to be determined. At all events, in the middle substage of the White River, or lower Oligocene, there is no evidence of more than a single phylum, from which the others were almost certainly derived, branching off from the main stem at different levels. First was given off the branch of the †giraffe-camels, then (or perhaps even earlier) that of the little †gazelle-camels, and, finally, the main stem bifurcated into the two phyla of the llamas and the true camels. The point of origin of the †gazelle-camels is still uncertain. [Illustration: FIG. 211.—The White River camel (_†Poëbrotherium labiatum_). Restored from a skeleton in the museum of Princeton University.] The typical White River genus (_†Poëbrotherium_) included a series of species which increased in size from the earlier to the later portions of the stage, but showed no such structural changes as to call for special notice. The larger of these species was somewhat taller than a sheep, but of much lighter proportions, with small, pointed head, long neck and body and long, very slender limbs and feet. The teeth were present in undiminished number, 44 in all; the lower incisors were small, simple, nearly erect and chisel-shaped, very different from the large, procumbent and shovel-like teeth of the modern genera, and the trenchant canines were much smaller than in the latter. The first premolar had an isolated position, the second and third were trenchant and much extended antero-posteriorly, quite as in many other groups of primitive artiodactyls. The molars, which were typically selenodont, were low-crowned in the upper jaw, but in the lower showed an incipient tendency to hypsodontism. The skull, by its shape and the characteristic narrowing of the face, immediately suggests the modern type, but differed in many details of structure, the most obvious of which were the incompletely closed orbits, the shallow and slender jaws, and the very large, hook-like process from the angle of the lower jaw, which, in greatly reduced form, is present in both of the Recent genera. The neck was relatively long, though by no means so long proportionately as it subsequently became, and the vertebræ had already acquired the peculiarity found in all the succeeding camels, of the exceptional position of the canal for the vertebral artery, save in the sixth vertebra, where it pierced the transverse process, as in mammals generally; the odontoid process of the axis was neither spout-like nor peg-like, but of intermediate form, convex below and flat above. The