THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 331 



Mastodon (Tdralophodon) latidens, molars with four transverse crests. 

 Mastodon (Trilophodon) falconeri, molars with three transverse crests. 

 Mastodon (Trilophodon) pandionis, molars with three transverse crests. 

 Mastodon (Trilophodon) pahviyidiais, molars with three transverse 



crests, a variety of Trilophodon angustidens. 

 Mastodon (Trilophodon) angustidens. 



A diphyletic subdivision of the mastodons is: (1) into those forms in 

 which the transverse crests are composed of conic nipples, or tubercles, 

 with accessory cones, forming trefoils, namely : M. (Tetralophodon) longiro- 

 stris, M. pentelici, M. (Tetralophodon) sivalensis; and (2) those in which we 

 find simple, sharply defined transverse crests without accessory cones, M. 

 (Trilophodon) turicensis, M. (Trilophodon) borsoni. 



The trilophodont species belong in the same group with the M. (Trilo- 

 phodon) borsoni and the M. (Trilophodon) turicensis, characteristic of the 

 Upper Miocene of Europe, while the tetralophodont mastodons are related 

 to the M. (Tetralophodon) longirostris of Europe. It will be recalled (p. 254) 

 that the trilophodont T. angustidens has large lower incisors, while the 

 trilophodont T. turicensis has small lower incisors. In all the tetralopho- 

 donts of Europe and Asia, including India and China, the upper incisors 

 are without enamel, while the lower incisors are small or wanting, and the 

 lower jaw is correspondingly abbreviated; this abbreviation of the lower 

 jaw is a characteristic feature of the Pliocene mastodons. 



A progressive character not mentioned above is the addition of cement 

 to the grinding teeth, as in horses and other grazers; this we first discover 

 in certain of the tetralophodonts (7^. perimensis), and it increases in the 

 stegodonts (S. cliftii, S. bombifrons). 



It is a remarkable feature of the proboscideans that from the geologically 

 low'Cst to the highest or most recent forms they all use their six grinding 

 or premolar-molar teeth on each side at some period of life; while the lower 

 forms employ four and even five grinders at once, it is a distinctive, pro- 

 gressive character of the highest forms to employ their upper and loAver 

 grinders successively, two pairs at a time, and finally one pair at a time, 

 the anterior grinders being used in youth and the posterior in old age. 



The stage E. (Loxodonta) planifrons is the final transition between the 

 mastodontoid, or crested, and the elephantoid, or plated type; the grinders 

 consist of high, thin transverse crests with intermediate valleys completely 

 filled with cement. This animal is much more primitive than the E. anli- 

 quus, or straight-tusked elephant of the Lower Pleistocene of Europe, the 

 closest counterpart of E. antiquus being found in the E. namadicus, which 

 is recorded in the Low-er Pleistocene of India. 



It is obvious from this review that part of the mastodons of India 

 resemble the Middle and Upper Miocene mastodons of Europe, and it 

 would appear that the Upper Pliocene of India (? and of Africa) witnessed 



