304 MAMMALIA. 



other species the same teeth have four ridges ; the various forms have 

 thus been subdivided into Trilophodon and Tetralophodon respectively. 

 No subdivision of the genus Mastodon, however, is satisfactory and cogent, 

 and it seems best to employ the term in a wide sense. The earliest species 

 hitherto discovered are Trilophodonts from the Middle Miocene of Europe 

 (M. turicensis and M. angustidens), and the latter is known by a nearly 

 complete skeleton from the Department of Gers in France (fig. 175). Both 

 Trilophodonts and Tetralophodonts are found in the Upper Miocene of 

 Europe and North America, while a few Trilophodont molars have been 

 met with in a formation believed to be of still more ancient date in 

 Montana, U.S.A. Mastodon longirostris (fig. 174) is a well-known Tetra- 

 lophodout from the Lower Pliocene of Eppelsheim (Hesse Darmstadt) 

 and other European localities, showing much-mammillated ridges on the 



FIG. 174. 



Mastodon lo-ngirostris ; left upper milk-molars, two-thirds iiat. size. L. 



Pliocene ; Eppelsheim, Hesse Darmstadt. (From Gaudry's Enchaine- 

 ments, after Kaup.) 



teeth ; and closely similar forms are known by fragmentary remains from 

 the Lower Pliocene of Pikermi, near Athens, the Island of Samos, and 

 Maragha in Persia. Mastodon arvernensis is another Tetralophodont from 

 the Upper Pliocene of the Auvergne, France, and the Val d'Arno, Tuscany. 

 Pliocene species of Mastodon are also abundant in the Siwalik formation of 

 India, and teeth have been discovered in China and Algeria. Several well- 

 preserved teeth are known from the Pliocene Crag deposits of Norfolk and 

 Suffolk. Before the close of the Pliocene period the genus seems to have 

 become extinct in Europe, but some species survived in the Pleistocene 

 both in North and South America. The best-known American Pleistocene 

 species is a Trilophodont (M. americanus or M. okiotwus), of which entire 

 skeletons are often discovered mired in the salt-marshes of the United 

 States, sometimes in association with flint implements. Young individuals 

 exhibit rudimentary lower tusks, but these are lost in the adult. The 

 South American species are also Trilophodonts and range as far south as 



