_Sirenia_ (sea-cows).--These are represented by two extinct genera, _Halitherium_ and _Trachytherium_. Several species of the former have been discovered, but the latter has occurred in France only, and its affinities are doubtful. _Ungulata._--Horses are represented by _Hipparion_ and _Anchitherium_, the latter occurring in both Upper and Lower Miocene and Eocene; while _Hipparion_, which is more nearly allied to living horses, first appears in the Upper Miocene and continues in the Pliocene. _Hippotherium_, in the Upper Miocene of the Vienna basin, forms a transition to _Paloplotherium_, an Eocene genus of Tapiridæ or Palæotheridæ. Tapirs, allied to living forms, occur in both Upper and Lower Miocene. Rhinoceroses are still found in the Upper Miocene, and here first appear the four-toed hornless rhinoceros, _Acerotherium_. The Suidæ (swine) are rather numerous. _Sus_ (wild boar) continued as far back as the Upper Miocene; but now there first appear a number of extinct forms which have been named _Hyotherium_, _Palæochoerus_, _Choeromorus_, all of a small or moderate size; _Hyopotamus_, nearly as large as a tapir; and _Anthracotherium_, nearly the size of a hippopotamus and, according to Dr. Leidy, the type of a distinct family. _Listriodon_, from the Upper Miocene of the Vienna basin, is sometimes classed with the tapirs. We now come to a well-marked new family of Artiodactyle or even-toed Ungulata, the _Anoplotheriidæ_, which consisted of more slender long-tailed animals, allied to the swine but with indications of a transition towards the camels. The only genera that appear in the Miocene formation are, _Chalicotherium_, nearly as large as a rhinoceros, of which three species have been found in Germany and France; and _Synaphodus_, known only from its teeth, which differ somewhat from those of the _Anoplotherium_ which appears earlier in the Eocene formation. Another extinct family, _Amphimericidæ_ or _Xiphodontidæ_, is represented by two {120}genera, _Cainotherium_ and _Microtherium_, in the Miocene of France. They were of very small size, and are supposed to be intermediate between the Suidæ and Tragulidæ. The Camelopardalidæ, or giraffes, were represented in Europe in Miocene times by the gigantic _Helladotherium_, which has been found in the south of France, and in Hungary, as well as in Greece. The chevrotains (Tragulidæ) are represented by the extinct genus _Hyomoschus_. The Cervidæ do not seem to have appeared in Europe before the Upper Miocene epoch, when they were represented by _Dorcatherium_ and _Amphimoschus_, allied to _Moschus_, and also by true _Cervus_, as well as by small allied forms, _Dremotherium_, _Amphitragalus_ (in the Lower Miocene), _Micromeryx_, _Palæomeryx_, and _Dicrocerus_.