PERISSODACTYLA. 327 



other hand, there are two of these appendages, also placed 

 upon the nasal bones in the median line of the head, the 

 posterior horn being shorter than the anterior, or differing 

 from it in form. While the true Ehinoceroses have invariably 

 a median horn or horns, we shall see shortly that there 

 existed allied types (viz., Colonoceras and Dicerathermm) in 

 which the horns were paired. 



Even excluding Acerotherium, we find true forms of 

 Mhinoceros in existence as early as the Miocene period 

 (B. Schleiermacheri, R. imcliygnatlmis, &c.) ; and there are 

 numerous fossil species in the Pliocene and Post-Pliocene 

 deposits of the Old World. In the New World the genus 

 Bliinoceros itself does not appear to be represented, but the 

 Miocene and Pliocene deposits of North America have yielded 

 several species of Acerotherium. Of the fossil forms of 

 Bliinoceros, the most important are B. tichorhinus, B. mega- 

 rliinus, B. hemitcBcJius, and B. Mruscus. 



The Bliinoceros ticlwrliinus (fig. 630) is generally known 

 as the " Woolly Pthinoceros," from its possession of a woolly 

 covering. Its skin was foldless, and it possessed two horns, 

 of which the anterior one was very large. The limbs are 

 extremely stout, and the nostrils are completely separated 

 by an osseous septum. B. tieliorhinus is essentially a north- 

 ern form, and has the same distribution in space as the 

 Mammoth, except that it did not cross Behring's Straits, and 

 is therefore not found in America. In time, it is younger 

 than the Mammoth, not being found in the pr?e-glacial forest- 

 bed of Norfolk, and occurring for the first time in the Lower 

 Brick-earths of the Thames valley (prse-glacial, but younger 

 than the " forest-bed "). It is therefore essentially a Post- 

 glacial Mammal, and it is mainly found in quaternary cave- 

 deposits and valley-gravels. 



The Bliinoceros hemitmclius of Falconer ( = the B. lejJtorJiimis 

 of Owen) is also provided with two horns, but is of a much 

 more slender build than the Tichorhine form. The nasal 

 bones are slender, and the nostrils are separated by a 

 partially - ossified septum. The adult animal possesses 

 neither incisor nor canine teeth. Like the preceding, B. 

 hemitceclms is exclusively Post-Pliocene in its distribution. 



