DESCRIPTION OF PLATES. 5 



■worn out ; they were four in number. Mastodon latidens is the form 

 most nearly allied to E. Cliftii, and, through that species, to the true 

 Elephants.— KM. 



Length of last tooth, 5"5 in. 



Fig. 9. — Mastodon Ohioticus. Vertical section of last upper molar. 

 Ir consists of four principal ridges and a small talon lobe. The ridges 

 are transverse, terminating in a trenchant edge ; the ivory segments are 

 in regular angular lobes ; the layer of enamel is of uniform thickness, 

 and the hollows between the ridges are very wide and open, being 

 almost rounded at the bottom. There is only an exceedingly thin crust 

 of cement, continued over the fangs in greater thickness. The common 

 plane of the grinding ridges of the crown is nearly horizontal. M. 

 Ohioticus constitutes the terminal link in the chain, and through 

 Dinotherium establishes a passage into the ordinary Pachydermata. — 

 B.M. 



Fig. 10 a. — Mastodon Sivalensis, from the Sewalik hills. Vertical 

 section of last upper molar. The ridges are more complex in their 

 composition than in M. latidens. The crown is bisected by a longitudinal 

 furrow, each division of the ridge being composed of a pair of contiguous 

 conical mammilla? placed more or less alternately. The hollows are in 

 consequence interrupted. There are five principal ridges, with a subor- 

 dinate ridge in front, and a talon ridge behind. Eight divisions of the 

 ivory may be counted in the figure, the smaller segments arising from 

 the direction in which the section has been made through the alternate 

 mammihaj. The ridges are approximated, and the enamel bears a 

 large proportion to the conical lobe of ivoiy which it invests. The 

 cement is entirely wanting, except in the bottom of the clefts. — B.M. 

 Length of tooth, 7 in. 



Fig. 10 b. — Mastodon Sivalensis. Vertical section of greater part 

 of last lower molar. The tooth differs from the corresponding upper 

 molar only in being complicated with an additional ridge. — B.M. 



Fig. 11. — Dinotherium Indicum (Falc), from Perim Island. Ver- 

 tical section of posterior ridge and talon of the penultimate lower 

 molar, left side. The internal structure exhibits the same agreement 

 with that of the European Dinotherium, as is indicated by the external 

 form. The only perceptible difference is, that the angle formed by the 

 ridge of the ivory is more acute, and the enamel thicker in the Indian 

 species. The centre is occupied by a rhomboidal core of arenaceous 

 matrix marking the form of the unossified pulp nucleus. This tooth 

 is described and figured in Dr. Falconer's Memoir on Perim Island 

 F -ils. 



Fig. 12. — Dinotherium giganteum (Kaup), from Eppelsheim. Ver- 

 tical section of entire penultimate lower molar, consisting of two 

 transverse crenulated ridges, and a talon ridge, while in the ecati- 

 valent molar of Mastodon Ohioticus there are three principal ridges. 

 Corresponding to the smaller number of divisions the ridges 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, however, is 

 the species most nearly allied to M. Ohioticus. — B.M. 



