_Chœropotamidæ._—In this family the molars are intermediate in structure between those of the _Suidæ_ and the next family. The upper ones have very broad crowns, with the five columns arranged as in _Anthracotherium_; while the premolars are not secant, and may be very large. The best known forms are the small _Cebochœrus_ of the Phosphorites of Central France; _Chœropotamus_ of the Upper Eocene, the type species of which was of the size of a large Pig, with the dental formula _i_ ³⁄₃, _c_ ¹⁄₁, _p_ ⁴⁄₃, _m_ ³⁄₃, and no distinctly selenodont structure in the molars; the much larger _Elotherium_, from the Upper Eocene and Lower Miocene of both the Old and New Worlds, which presents the very rare feature of the absence of a third lobe to the last lower molar; and the equally large _Tetraconodon_ of the Pliocene of India, in which this third lobe was present and the premolars were of enormous size. The remarkable North American Eocene genus _Achænodon_ should perhaps also be placed here. [Illustration: FIG. 112.—A right upper molar of _Merycopotamus pusillus_, Pliocene, India. (From the _Palæontologia Indica_.)] _Anthracotheriidæ._—The genera _Anthracotherium_ and _Hyopotamus_, of the upper Eocene and Miocene, have the typical Eutherian dental formula; the upper molars (Fig. 111) carrying three columns on the anterior and two on the posterior half of the crown, all of which are of a more or less decidedly selenodont structure. The mandible has a descending flange at the angle. The figured tooth (in which the antero-internal and antero-median columns are imperfect) may be compared with the diagram given in Fig. 5, p. 32, when the homology of the columns or tubercles will be at once apparent, the broken antero-median column representing the protoconule. Some of the species are of large size, while others are comparatively small. _Merycopotamus._—The genus _Merycopotamus_ of the lower Pliocene of India may be regarded as an Anthracotheroid which has lost the antero-median column to the upper molars (Fig. 112), so that these teeth are consequently quadrituberculate; and may thus be regarded as typical examples of the brachy-selenodont modification of molar structure.