This family, one of the strangest and most aberrant of ungulate groups, was very closely allied to the †oreodonts and by many authorities is included in the same family. The history of the successive steps of discovery, by which the structure of these extraordinary animals was gradually made plain, is much the same as in the case of the even more peculiar perissodactyl family of the †chalicotheres (p. 356). The various parts, found scattered and at long intervals of time, had been referred to no less than three different mammalian _orders_! for, until the discovery of †chalicothere skeletons gave the clue, no one imagined that such discordant parts could belong to the same animal. [Illustration: FIG. 205.—Skull of _†Agriochœrus latifrons_, White River. (After Wortman.)] [Illustration: FIG. 206.—_†Agriochœrus antiquus_, White River. Restored from a skeleton in the American Museum of Natural History.] The †agriochœrids had a very much shorter career than the allied family of the †oreodonts, extending only through the upper Eocene and the Oligocene (Uinta to John Day, inclusive); and only two genera of the family are yet known, _†Agriochœrus_ of the John Day and White River, and _†Protagriochœrus_ of the Uinta. In the former the teeth were not in a continuous, closely crowded series, but there were open spaces behind the upper canine and first lower premolar; the same exceptional character of the lower teeth which was found in the †oreodonts was repeated in the present family, the canine assuming the form and functions of an incisor and the first premolar those of the canine; the upper incisors were extremely small and were shed in the adult, just as in the true ruminants. The molars had the selenodont pattern, but the upper molars were very different in shape from those of the †oreodonts, resembling rather those of the †anthracothere _†Bothriodon_ (see p. 370). Another difference from the †oreodont dentition was that the last lower premolar had acquired the molar form and the last upper one nearly so, a very unusual feature among the artiodactyls. The skull was almost exactly like that of the White River †oreodonts, save in a few details; the face was somewhat longer, the orbit was open behind and there was no glandular pit on the face in front of the eye. The neck was short and the body long, and the backbone in the region of the loins very stout, the vertebræ of this region having much resemblance to those of the great cats, as though _†Agriochœrus_ were an agile and powerful leaper. Another likeness to the cats was in the very long and heavy tail, which was much longer than in the †oreodonts, and its vertebræ were hardly distinguishable from those of a Leopard. The limbs were relatively longer than those of the †oreodonts and the separate bones had a suggestive likeness to those of carnivores, and, more specifically, of cats. The feet, save in one particular, were not only artiodactyl, but also characteristically