THE MIOCENE PERIOD. 333 



verse plates of enamel united together by ivory ; and by the 

 process of mastication, the teeth become worn down to a flat 

 surface, crossed by the enamel-ridges in varying patterns. 

 These patterns are different in the different species of Ele- 

 phants, though constant for each; and they constitute one of 

 the most readily available means of separating the fossil 

 forms from one another. Of the seven Miocene Elephants 

 of India, as judged by the characters of the molar teeth, 

 two are allied to the existing Indian Elephant, one is related 

 to the living African Elephant, and the remaining four are in 

 some respects intermediate between the true Elephants and 

 the Mastodons. 



The Mastodons, lastly, though quite elephantine in their 

 general characters, possess molar teeth which have their crowns 

 furnished with conical eminences or tubercles placed in pairs 

 (fig. 247, B), instead of having the approximately flat surface 

 characteristic of the grinders of the Elephants. As in the 

 latter, there are two upper incisor teeth, which grow perma- 

 nently during the life of the animal, and which constitute great 

 tusks; but the Mastodons, in addition, o'ften possess two lower 

 incisors, which in some cases likewise grow into small tusks. 

 Three species of Mastodon are known to occur in the Upper 

 Miocene of the Siwalik Hills of India; and the Miocene de- 

 posits of the European area have yielded the remains of four 

 species, of which the best known are the M. longirostris and the 

 M. angustidens. 



Whilst herbivorous Quadrupeds, as we have seen, were 

 extremely abundant during Miocene times, and often attained 

 gigantic dimensions, Beasts of Prey (Carnivora) were by no 

 means wanting, most of the principal existing families of the 

 order being represented in deposits of this age. Thus, we find 

 aquatic Carnivores belonging to both the living groups of the 

 Seals and Walruses; true Bears are wanting, but their place 

 is filled by the closely-allied genus Amphicyon, of which various 

 species are known; Weasels and Otters were not unknown, 

 and the Hycunictis and Ictitherium of the Upper Miocene of 

 Greece are apparently intermediate between the Civet-cats and 

 the Hyaenas; whilst the great Cats of subsequent periods are 

 more than adequately represented by the huge " Sabre-toothed 

 Tiger" (Machairodus), with its immense trenchant and serrated 

 canine teeth. 



Amongst the Rodent Mammals, the Miocene rocks have 

 yielded remains of Rabbits, Porcupines (such as the Hystrix 



