556 



UNGULATES. 



The Mastodons. 



Genus Mastodon. 



The above-mentioned stegodont elephants so closely connect the genus Elephas 

 with the extinct animals known as mastodons, that the division between the two 

 genera is a somewhat arbitrary one. It is noteworthy that the species of mastodon 

 most nearly related to the stegodont elephants are found in the same regions as 



THE LAST LEFT UPPER MOLAR TEETH OF TWO SPECIES OP INDIAN MASTODONS. 



The upper figure (§ nat. size) belongs to M. lalidens; and the lower (J nat. size) to M. 

 cautleyi. In the specimen represented in the upper figure the first two ridges are 

 partially worn, while in the lower one they are intact. 



the latter, from which we may infer that the evolution of the elephants from the 

 mastodons took place in South-Eastern Asia. 



Mastodons are distinguished by their molar teeth, as shown in the accompanying 

 figure and the one on p. 557, having comparatively few transverse ridges, winch 

 are low, and more or less completely divided by a longitudinal cleft into inner and 

 outer columns. These ridges are separated by valleys in which there is little or 

 no cement; and when worn down by use they exhibit more or less trefoil-shaped 

 surfaces of ivory, quite different from the elongated ellipses formed in those of the 



