328 OEDERS OF MAMMALIA. 



and is found in cave-deposits and in the Thames valley 

 Brick-earths. 



The Rhinoceros megarhinus of Christol ( = the JR. Icptorhinus 

 of Cuvier and Falconer) is also bicorn, and resembles R. 

 hemitcechus in being of comparatively slender build. It is 

 distinguished, however, by the enormous development of the 

 nasal bones and the absence of the " cloison " or bony parti- 

 tion between the nostrils. This form (fig. 627) is found in 

 the Pliocene beds of Italy and France, and also occurs in 

 the pr?e-giacial forest-bed of Cromer and the Lower Brick- 

 earths of the Thames valley. 



Rhinoceros Etruscus (fig. G26, a) is also bicorn, and has 

 the nostrils partially separated by a " demi-cloison " or in- 

 complete bony partition, which " strengthened the basement 

 of the anterior horn." This species is found in deposits of 

 Pliocene age, and occurs also in the Post-Pliocene (as in the 

 Cromer forest-bed). 



In addition to Rhinoceros and Accrothcrium, the Tertiary 

 rocks have yielded various other forms of Rkhioccriclm, some 

 of which depart very widely from the general type. The 

 oldest known forms are Amynodon and Colonoccras, both of 

 which are found in the Eocene Tertiary of North America. 

 In Amynodon there were no horns, and there were both 

 upper and lower canines, while none of the praemolars were 

 like the molars. Colonoccras, again, is very closely allied to 

 the Tapiroid genus Hyrachyus, but it has the curious char- 

 acter that the nasal bones carried two very rudimentary 

 osseous protuberances for the support of a pair of minute 

 horns ; these appendages, however, being placed symmetrically 

 on the sides of the head, instead of being situated one behind 

 each other in the middle line. The possession of symmetri- 

 cally-placed transverse horns is, however, a more conspicuous 

 feature in the Miocene genus Diecratherium, which nearly 

 equalled the existing Rhinoceroses in point of size, and 

 closely resembled them in other structural characters, except 

 that the fore-feet are four-toed. The genus is North American, 

 as is also the curious Hyracodon of the Miocene, in which 

 horns were completely wanting, and in which there is the 



