THE MIOCENE PERIOD. 321 
very large size, and are each composed of a number:of trans- 
verse plates of enamel united together by ivory; and by the 
Fig. 247.—A, Molar tooth of Zlephas planifrous, one-third of the natural size, show- 
ing the grinding surface—from the Upper Miocene of India; B, Profile view of the 
last upper molar of Mastodon Sivalensis, one-third of the natural size—from the Upper 
Miocene of India. (After Falconer.) 
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 MMastodons, lastly, though quite elephantine in their 
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