Amongst the Even-toed Ungulates, we may note the occurrence of Swine (Suida), of forms allied to the Camels (Camelidoe), and of various kinds of Deer (Cervidoe); but the most interesting Pliocene Mammal belonging to this section is the great Hippopotamus major of Britain and Europe.  This well-known species is very closely allied to the living Hippopotamus amphibius of Africa, from which it is separated only by its larger dimensions, and by certain points connected with the conformation of the skeleton.  It is found very abundantly in the Pliocene deposits of Italy and France, associated with the remains of the Elephant, Mastodon, and Rhinoceros, and it survived into the earlier portion of the Post-Pliocene period.  During this last-mentioned period, it extended its range northwards, and is found associated with the Reindeer, the Bison, and other northern animals.  From this fact it has been inferred, with great probability, that the Hippotamus major was furnished with a long coat of hair and fur, thus differing from its nearly hairless modern representative, and resembling its associates, the Mammoth and the Woolly Rhinoceros.

[Illustration:  Fig. 250.—­Third milk-molar of the left side of the upper jaw of Mastodon Arvernensis, showing the grinding surface.  Pliocene.]

Passing on to the Pliocene Proboscideans, we find that the great Deinotheria of the Miocene have now wholly disappeared, and the sole representatives of the order are Mastodons and Elephants.  The most important member of the former group is the Mastodon Arvernensis (fig. 250), which ranged widely over Southern Europe and England, being generally associated with remains of the Elephas meridionalis, E. antiquus, Rhinoceros megarhinus, and Hippopotamus major.  The lower jaw seems to have been destitute of incisor teeth; but the upper incisors are developed into great tusks, which sometimes reach a length of nine feet, and which have the simple curvature of the tusks of the existing Elephants.  Amongst the Pliocene Elephants the two most important are the Elephas meridionalis and the Elephas antiquus.  Of these, the Elephas meridionalis (fig. 251) is found abundantly in the Pliocene deposits of Southern Europe and England, and also survived into the earlier portion of the Post-Pliocene period.  Its molar teeth are of the type of those of the existing African Elephant, the spaces enclosed by the transverse enamel-plates being more or less lozenge-shaped, whilst the curvature of the tusks is simple.  The Elephas antiquus (fig. 252) is very generally associated with the preceding, and it survived to an even later stage of the Post-Pliocene period.  The molar teeth are of the type of the existing Indian Elephant, with comparatively thin enamel-ridges, placed closer together than in the African type; whilst the tusks were nearly straight.

[Illustration:  Fig. 251.—­Molar tooth of Elephas meridionalis, one-third of the natural size.  Pliocene and Post-Pliocene.]