368 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



mammalian foot. The best-known genus of the order (Condy- 

 larthra), which comprised animals intermediate in size between the 

 opossum and tapir, is Phenacodus, from the Puerco and Wasatch 

 Eocene. 



Ungulata Perissodactyla (Odd-toed hoofed-animals). The 

 only modern representatives of the odd-toed ungulates are the 

 rhinoceros, horse (including the zebra and ass), and tapir. Of the 

 first some five or six species are known, which are generally re- 

 ferred to a single genus Rhinoceros, although by some authors 

 several distinct genera are recognised. The African species (R. 

 bicornis, R. keitloa(?), and R. simus, the so-called white rhinoceros), 

 all two-horned, occupy the greater part of the continent south of 

 the desert, while in Asia the species, both single- and double- 

 horned, range from the forest-covered foot-hills of the Himalayas 

 through Farther India and the Malay Peninsula to Borneo, Java, 

 and Sumatra. The common Indian species, R. unicornis or In- 

 dicus, is now restricted in its range almost wholly to the terai re- 

 gion of Nepaul and Bhotan, and to the upper valley of the Brah- 

 maputra. Many species of rhinoceros, in part referable to the 

 genus or genera which contain the modern forms, are found fossil 

 in Europe and India in deposits dating from the Upper Miocene ; 

 Rhinoceros (Ceratorhinus) Schleiermacheri is Middle Miocene. The 

 hornless genus Aceratherium, which, on the American continent, is 

 preceded in the Upper Eocene by the somewhat rhinocerotic Amyn- 

 odon, and which may be considered as the first true rhinoceros, ap- 

 pears in the Lower Miocene deposits of both the Old and the New 

 World, and is looked upon by many as the ancestral type whence, 

 through migration and subsequent development, the existing and 

 Post-Pliocene (R. tichorhinus, &c.) species have been derived. The 

 American genus Aphelops, likewise hornless, belongs to a series of 

 deposits (Loup Fork) which by some authors are referred to the 

 Upper Miocene, and by others to the Lower Pliocene. Hyracodon, 

 a genus in many respects allied to the rhinoceros, but possessing 

 only three toes to the foot, is Lower Miocene or Oligocene (North 

 American). Singularly enough, no rhinocerotic form is found in 

 the New World above the Pliocene. None of the existing species 

 of rhinoceros antedate the Post-Pliocene period, although the 

 African bicorn type is actually represented in the earlier deposits 

 of Greece (R. pachygnathus) and the Siwalik Hills of India, which 



