Cyclopidius (synonymous with Brachymeryx) is a kind of pug form of Oreodon. The skull is short and broad, and the end of the snout a little turned up. The upper incisors are small and drop out early. On each side of the nasals is a large oval vacuity which is perhaps to be compared to the lateral deficiency to be found in other Artiodactyles. One species of this singular-looking form is appropriately called C. simus.
Other allied genera are Merychyus and Leptauchenia. The former extends as far down as the Lower Pliocene, and is thus one of the newest forms of Oreodontidae.
Agriochoerus[[213]] (Fig. 178) is placed in a separate sub-family from the types which have just been considered. It is Miocene in range. It differs from Oreodon and its closer relatives by the fact that the orbit is open behind and not closed. The most remarkable fact about this creature is that the terminal phalanges of the digits (five in the fore- and four in the hind-feet) being pointed, seem to suggest their encasement with claws rather than hoofs. The pollex, though small, seems to have been opposable. As with other Oreodonts, the molars are selenodont. The premaxillae are toothless—at least in adults, for two teeth are present in the
young. There are several species. Agriochoerus, like Oreodon and primitive Ungulates in general, had a long tail. The genus thus shows a mixture of ancient and specialised characters.
Fig. 178.—Skeleton of Agriochoerus latifrons. × ⅛. (After Wortman.)
The most ancient form of Oreodont is Protoreodon. This is Eocene, and became extinct during that period. It had a complete dentition, open orbit, and no lachrymal fossa. The fore-feet were five-toed, the hind four-toed.
Fam. Anoplotheriidae.—This family is entirely Eocene in point of time, and is unknown outside Europe. The dentition of the group is complete; the molars are seleno-bunodont, like those of the Anthracotheriidae. The bones of the carpus, tarsus, metacarpus and metatarsus are all free; the toes are four to two in number on each foot. The orbit is widely open behind. The tail is long, as in Xiphodon, etc.
These general characters only just serve to differentiate the family; but they illustrate its archaic character, in which it resembles the Xiphodontidae, and even more the Anthracotheriidae. A survey of some of the genera which have been assigned to the family will bring out other features in the organisation of these very ancient Artiodactyles.