_C._—Two well-marked species of African Swine have been with more reason separated under the name of _Potamochœrus_. The dentition differs from that of the true _Sus_, inasmuch as the anterior premolars have a tendency to disappear; sometimes in adult specimens the first upper premolar is retained, but it is usually absent, as well as the first and often the second lower premolars. The molar teeth are also less complex: the last especially having a much less developed talon. There are likewise characteristic cranial differences. The two species are very distinct in outward appearance and coloration. One is _S. africanus_, the South African River-Hog, or Bosch-Vark, of a gray colour, and the other _S. porcus_, the West African Red River-Hog (Fig. 107), remarkable for its vivid colouring and long pencilled ears. It should be noted that the young of both these species, as well as of the pigmy _S. salvanius_, present the striped character of the true _Sus_, a strong indication of close affinities, whereas in all the following forms this is absent. [Illustration: FIG. 107.—The Red River-Hog (_Sus porcus_). From Sclater, _Guide to Animals in Zoological Society’s Gardens_, 1883, p. 183.] The genus _Sus_, in the above extended sense, is well represented in the Tertiaries of the Old World from the period of the Lower Pliocene upwards. In the Pliocene and Pleistocene of India _S. falconeri_ and _S. karnuliensis_ are characterised by the extremely complex structure of the molars, in which they show decided signs of approximation to the Wart-Hogs; the same feature being exhibited by _S. phacochœroides_ of the Algerian Pliocene. _S. titan_ and _S. giganteus_, of the Indian Pliocene, together with _S. antiquus_ and _S. erymanthius_, of the corresponding European deposits, are very large species characterised by their comparatively simple molars; _S. titan_ being fully as large as a Tapir. _S. hysudricus_ of the Pliocene of India, and _S. palæochœrus_ of that of Europe, are smaller allied species not improbably related to _S. andamanensis_, with which they agree in molar structure. _S. arvernensis_, of the Upper Pliocene of France, appears to be allied to _S. africanus_; while in the diminutive _S. punjabiensis_ of the Pliocene of North-Western India we probably have the direct ancestor of _S. salvanius_. [Illustration: FIG. 108.—Head of Babirusa (_Babirusa alfurus_).]