The geographical distribution of animals, with a study of the relations ...

;chap, vi.] MAMMALIA OF THE OLD WORLD. 119Cetacea (whales).—These occur frequently inthe Miocene deposits,four living, and five extinct genera having been describedbut these marine forms are not of much importance for ourpurpose.Sirenia (sea-cows).—These are represented by two extinctgenera, Halitherium and Trachytherium.Several species of theformer have been discovered, but the latter has occurred inFrance only, and its affinities are doubtful.Ungulata.—Horses are represented by Hipparion and Anchitherium,the latter occurring in both Upper and Lower Mioceneand Eocene ; while Hipparion, which is more nearly allied toliving horses, first appears in the Upper Miocene and continuesin the Pliocene.Hvppotherium, in the Upper Miocene of the Vienna basin,forms a transition to Paloplotherium, an Eocene genus of Tapiridaeor Palseotheridse. Tapirs, allied to living forms, occur inboth Upper and Lower Miocene. Ehinoceroses are still foundin the Upper Miocene, and here first appear the four-toed hornlessrhinoceros, Acerotherium. The Suidae (swine) are rathernumerous. Sus (wild boar) continued as far back as the UpperMiocene ; but now there first appear a number of extinct formswhich have been named Hyotherium, Palceochcerus,all of a small or moderate size ;Chceromorus,Hyopotamus, nearly as large as atapir ; and Anthracotherium, nearly the size of a hippopotamusand, according to Dr. Leidy, the type of a distinct family.Listriodon, from the Upper Miocene of the Vienna basin, issometimes classed with the tapirs.We now come to a well-marked new family of Artiodactyleor even-toed Ungulata, the Anop>lotheriidce, which consisted ofmore slender long-tailed animals, allied to the swine but withindications of a transition towards the camels. The only generathat appear in the Miocene formation are, Chalicotherium, nearlyas large asa rhinoceros, of which three species have been foundin Germany and France ;and Synaphodus, known only from itssomewhat from those of the Anoplotheriumteeth, which differwhich appears earlier in the Eocene formation.Another extinctfamily, Amphimericidce or Xiphodontidce, is represented by two