FAM. CAENOTHERIIDAE.--While the last family consisted of animals rather more akin to the Pigs, the present is more Pecorine in its characters. The molars are selenodont; but as in the Tragulidae the premolars are more of the nature of cutting teeth. The dentition, like that of so many of these early Ungulates, is complete, and the canines are not prominent. The feet are four-toed, the lateral toes not reaching the ground. The principal genus is the Eocene and Miocene _Caenotherium_. Of this genus there were a considerable number of species all European in range, and of small size--not more than a foot or so in length. Their small size is suggestive of the Chevrotains. In the skull the orbital cavity is nearly or quite surrounded by bone, and the tympanic bulla is large and inflated. A common feature of Artiodactyles, a failure of the nasals and maxillae to meet at the side of the face, is to be seen in this ancient forerunner of the Pecora. _Plesiomeryx_, also European, and from the same geological horizon, is a very closely allied form. FAM. XIPHODONTIDAE.--This family consists of slender, small Artiodactyles which are, like the Caenotheriidae, related to the Pecora. They are confined in their range to Europe. The type genus _Xiphodon_ has selenodont molars and elongated, slender, cutting premolars. The dentition was complete and the canines not highly developed. Like _Caenotherium_, {330} _Xiphodon_ was a hornless creature, but with only two toes, the two lateral digits being represented by the merest rudiments of metacarpals. The other metacarpals were unusually long. _Amphimeryx_ (also called _Xiphodontotherium_) is much more imperfectly known, but belongs to this family or to that of the Caenotheriidae. _Dichodon_ is another member of the same family. FAM. OREODONTIDAE.--This family, consisting of numerous genera, is limited to the North American continent. Its range in time is from the Eocene to the Lower Pliocene. The family as a whole is to be distinguished by a number of primitive characters. The dentition is complete; the feet are four- or even five-toed; the orbit is sometimes open behind. The canines of the lower jaw are not more pronounced than the incisors. The characteristics of the group will be further developed by a consideration of some of the principal genera which are included in this family.