ELEPHANT AND MASTODON. 85 



distinct section, agreeing in liaving the three molars which 

 precede the last, viz. the third deciduous molar and the 

 peunltimate and antepenultimate true molars, uniformly cha- 

 racterized by having their crown divided into three ridges in 

 both jaws; while the same teeth in the preceding group have 

 each a crown with/owr ridges. The teeth of M. Andium and 

 M. ancj'ustidens are not included in the plates of sections. 

 Following the same serial arrangement which has been ob- 

 served throughout, their place would be between M. Sivalensis 

 and If. Ohioticus, the latter of which forms the terminal link 

 in the chain, establishing the nearest passage into Dino- 

 therium, and through that genus into the ordinary Pachyder- 



Fig. 3 of PI. YI. and fig. 3 of PI. YII. (PL III. figs. 11 and 

 12, r.A.S.), represent sections of the penultimate lower 

 molar of two species of Dinotlierium, the former a fragment, 

 showing the posterior half of the tooth in D. Indicum, and the 

 latter the whole tooth in Z>. giganteum. The sections exhibit the 

 same arrangement of the dental substances as in M. Ohioticus. 

 The tooth, PI. VII. fig. 3, consists of two transverse crenulated 

 ridges, and a talon ridge, while in the equivalent molar of 

 M. Ohioticus there are three principal ridges. Corresponding 

 to the smaller number of divisions, the ridges in D. giganteum 

 are more widely separated, less elevated, and broader at their 

 base, while the interspaces are also wider and more open 

 than in the North American mastodon; the layer of enamel 

 is of similar thickness, and there is no appreciable crust of 

 cement. The correspondence is followed out in the form of 

 the subordinate heel ridge. D. Indicum is the species which 

 is most nearly allied to M. Ohioticus ; and all the ascertained 

 evidence regarding it tends to prove that it belonged to a 

 true Proboscidean Pachydermatous genus like the latter. 



§ 3. On the Succession of the Molars, and their Chaeactees as 



INDICATING SeCTIONAI GrOUPS OF SpECEES. 



The molar teeth, developed dtu-ing the course of life in the 

 ordinary Pachydermata, are divisible into three weU-marked 

 sets; the milk or deciduous molars, the false molars or succes- 

 sional j)remolars, and lastly,' the true molars. The milk teeth 

 are so distinct, in their transitory character, from the permanent 

 series, that the consideration of the former is usually omitted 

 in the construction of generic definitions ; but in Mastodon 

 and Elephas, the succession of the teeth is so modified, and 

 the premolars are so completely or partially suppressed, that 

 the triple division is rendered very obscure, and it has 

 commonly been found necessary by systematic authors, to 



