ELEPHANTID^E. 15 



may be traced — the one (in which there is a tendency of the valleys 

 of the molars to he much blocked and their columns to be ranged 

 alternately) passing through M. pandionis and M. perimensis to 

 M. sivalensis and M. arvernensis, and the other (in which the valleys 

 remain more open and the columns of the ridges run straight across 

 the crowns) passing through M. longirostris and M. latidens to 

 Elephas clifti, and then through the higher stegodont forms to the 

 true Elephants ; while there are signs that some of the middle forms 

 of these two branches were mutually connected. 



The genus has been divided into groups by Falconer according to 

 the number of ridges in the cheek-teeth ; and this division indicates 

 the degree of evolution of its members. Cope * proposes to split the 

 genus into three (Mastodon, Dibelodon, and Tetrabelodon), according 

 to the presence or absence of enamel-bands in the upper incisors, 

 and of lower incisors ; but such division, even if it can be made, 

 directly traverses the evolutionary grouping of Falconer. 



A. Trilophodont Group. 

 The " intermediate " molars usually carry three, and the last molar 

 four ridges, the full ridge-formula being : — Mm. \ ' \ '\ , M. I ' I ' 3 - 



Mastodon americamis (Cuvier 2 ). 



Syn. 3 Elephas americanus, Cuvier 4 . 



Mammuth ohioticus, Blumenbach 5 . 

 Mastodon yiganteus, Cuvier 6 . 

 Mastodon maxinms, Cuvier 7 . 

 Tetracaulodon mastodontoideus, Godman 8 . 

 Tetracaulodon brevirostris, Kaup 9 . 

 Mastodon jeffersoni, Hays 10 . 

 Mastodon cuvieri, Hays u . 



The valleys of the molars are completely open, and the transverse 

 ridges straight, but with a distinct median longitudinal cleft ; the worn 



1 Proc. Amer. Phil. Soc. vol. xxii. p. 5 (1884). 



2 Table Elem. d'Hist Nat. p. 149 (1798), Elephas. 



3 For fuller synonymy, see Leidy, Journ. Ac. Nat. Sci. Philad. ser. 2, vol. vii. 

 p. 392 (1869). 



4 Loc. cit. 



5 Handbuch d. Naturgeschicbte, 6th edit. p. 698 (1799). 



6 Eegne Animal, 1st ed. vol. i. p. 233 (1817). 



7 Ossemens Fossiles, 2nd ed. vol. v. pt. 2, p. 527 (1824). 



8 Trans. Amer. Phil. Soc. ser. 2, vol. iii. p. 484 (1830). 



9 Isis, vol. xxv. p. 630 (1832). 



10 Trans. Amer. Phil. Soc. ser. 2, vol. iv. p. 334 (1834). « Loc. cit. 



