UNGULATA. 



the Argentine province of Buenos Aires. Many of the forms seem to 

 have rivalled the largest elephants in size. 



Elephas (figs. 171 c, D, 176). Some of the more highly specialized 

 types of Mastodon pass almost insensibly into the more generalized forms 

 of true elephants, and it is difficult to find a constant difference between 

 the two genera. The ridges of the molars, however, are always more 

 numerous in Elephas, and they are usually deep plates, while the inter- 

 vening clefts or valleys are filled with cement. The lowest grade, known 

 only from the Pliocene of India, Burmah, Java, the Philippine Islands, 

 China, and Japan, is named Stegodon, the ridges on its teeth being 

 roof-shaped in section and the valleys being only partly filled with cement. 

 The number of the ridges on the "intermediate molars" of this form 

 varies from 6 to 8. The next grade, named Loxodon in allusion to the 



FIG. 175. 



Mastodon angustidens ; restoration of skeleton by A. Gaudry, one-fiftieth nat. 

 size. M. Miocene; Gers, France. 



lozenge-shaped areas often observed when the ridges are worn, has the 

 "intermediate molars" with from 7 to 9 ridges, deeper and more com- 

 pressed. The most advanced grade, Euelephas, may exhibit the "inter- 

 mediate molars" with as many as 12, 15, and 16 ridges respectively, these 

 being now indeed closely adpressed deep plates. The sub-genus Stegodon, 

 as already remarked, is exclusively Asiatic, and the finest known specimens 

 are from the Siwalik Formation of India. A skull of Elephas (Stegodon) 

 ganesa in the British Museum exhibits a pair of tusks nearly 3 metres in 

 length. The sub-genus Loxodon survives in the existing African elephant 

 (Elephas africanu*), and has extinct representatives widely distributed in 

 the Pleistocene and later Pliocene deposits of Europe, as also in the Lower 

 Pliocene of India. The extinct Indian species, E. planifrons, is unique so 

 far as known in exhibiting two premolars to replace the milk-molars in 

 both jaws. The European Upper Pliocene species, E. meridionah's, is 



w. 20 



