_Cænotheriidæ._—The typical representatives of this family are small animals not larger than the Chevrotains, with the full complement of teeth, generally no marked gap in the series, and the crowns of the upper molars carrying two columns on the anterior and three on the posterior half of the crown—precisely the reverse of the arrangement obtaining in the _Anthracotheriidæ_. The known forms are from the Upper Eocene and Lower Miocene of Europe. In _Cænotherium_ the molars are selenodont, while they are bunodont in _Dichobunus_. _Homacodon_, of the Bridger Eocene of the United States, is closely allied to the latter. The first lower premolar of _Dichobunus_ assumes the form and function of a canine. _Spaniotherium_ (_Metriotherium_) is a much larger form, in which the molars are not unlike those of _Anthracotherium_, if the arrangement of the cusps were reversed; it occurs in the Eocene Phosphorites of France. It is suggested that the _Tylopoda_ may have originated from this group. _Tapirulus_ is a small Eocene Artiodactyle with the columns of the upper molars, which are somewhat like those of _Hyopotamus_, tending to form transverse ridges; its family position is uncertain. _Dichodontidæ._—The European genera included in this family all have quadritubercular selenodont molars, and show signs of approximating more or less closely to existing types. _Dichodon_, from the Upper Eocene and Lower Miocene, has the full complement of teeth, which show no diastema, and have low crowns. The fourth upper premolar has four columns, like the true molars, and the corresponding lower tooth three complete lobes; these features being unknown in any other Selenodonts. In _Lophiomeryx_, of the same beds, the somewhat higher crowns of the molars approximate to those of the _Cervidæ_, but the hinder lobes of the upper ones are imperfectly developed; the genus may be allied, to the _Tragulidæ_. In the small _Gelocus_, of the Lower Miocene, the molars are not unlike those of _Dichodon_; but the navicular and cuboid bones of the tarsus were fused together, and the metatarsals had united to form a “cannon-bone,” although the metacarpals still remained distinct. It is not improbable that upper incisors were wanting; and it has been suggested that we have in this genus the ancestral type of the _Tragulidæ_ and _Cervidæ_. TYLOPODA. _Family_ CAMELIDÆ.