MASTODON. 31 



development is Mastodon arvernensis, which is found in Europe Pier- 

 in Pliocene deposits ; in it the lower incisors seem to be entirely 37^40 

 Avanting, and the anterior molars have four transverse ridges. 



Fig. 18. 



Mandible of a young individual of Mastodon americanus showing the small 

 remnants of the lower incisors. In the adult these are lost. From a 

 Pleistocene Deposit, North America. About 1 nat. size. 



A nearly allied species, M. sivalensis (fig. 20), from the Pliocene 

 of India, is notable as showing a tendency to acquire five ridges 

 to its molars. 



The region in which the passage from the Mastodons to the 

 true elephants occurred, seems to have been Southern Asia, 



