body was long and light, and the ribs were much more slender than in the Recent genera. The fore and hind limbs, which were of nearly equal length, were very slender; the humerus had a single bicipital groove; the fore-arm bones were fully coössified and in the lower leg only the two ends of the fibula remained. The feet were already in the stage of development which persisted through the lower Miocene in all of the phyla, with two separate digits and nodular remnants of two others, and deer-like hoofs. It would be of interest to compare this little White River camel with its contemporary genus of horses, _†Mesohippus_, and to observe in how many respects they have followed a parallel course, and how nearly _†Poëbrotherium_ occupied the same position with reference to the modern camels and llamas as _†Mesohippus_ did to the Recent horses; but such a comparison would involve too many technicalities to be profitably undertaken here. Suffice it to say that in many details there was a genuine parallelism in the progress of these two widely separated families from a polydactyl ancestry towards an extreme of digital reduction, ending in the horses in the single-toed and in the camels in the two-toed foot. The members of the two series kept nearly equal pace in their slow progress, with the camels a little in advance, since they were the first to attain the modern state of development in the height of the teeth and the structure of the feet, though eventually the horses surpassed them in both respects.