84 FAUXA A^^TIQUA SIYALEXSIS. 



except in the bottom of tlie clefts. This tooth measures 

 about seven inches in leug-th. 



Fig. 10 fe, PL HI., F.A.S., shows a section of a fragment 

 comprising the gTeater part of the last lower molar of the 

 same species. There is a similar alternate arrangement of the 

 mammiUse, and the tooth differs fi'om the corresponding upper 

 molar only in being complicated with an additional iddge. 



The teeth of this species bear an exceedingly close resem- 

 blance to certain of the Eui-opean fossil grinders, which have 

 beendescribed under the indefinite name of M. angustidens. Tlie 

 three species, M. latidens, 31. Arvernensis, and M. Sivalensis, 

 with perhaps a fourth, of doubtful determination, constitute 

 a particular section of Mastodon, characterized by the same 

 numerical division of the crown ridges in the last deciduous 

 molar, and in the first and second true molars in both jaws. 



Pl.YII. fig. 2 (PL III. fig. 9, r.A.S.), as previously described, 

 represents a section of the last upper molar of Mastodon 

 Ohioticus. It consists of four principal ridges and a small 

 talon lobe. The successively increasing simplicity of form 

 which has been traced from E. insignis attains its extreme 

 limit in the molars of this species. The ridges are trans- 

 verse, terminating in a trenchant edge ; the ivory segments 

 are in regular angular lobes, the layer of enamel is of uni- 

 form thickness, and the hollows between the ridges are very 

 wide and open, being almost rounded at the bottom. The 

 cement is present only in an exceedingly thin crust, con- 

 tiiuied over the fang^s in gfreater thickness. The common 

 plane of the grinding ridges of the crown is nearly horizontal, 

 while it is more or less convex in all the previously noticed 

 species. It has not been deemed necessaiyto give a delinea- 

 tion of the section of an inferior molar, which differs in no 

 respect fi-om the upper, except in being complicated with an 

 additional ridge. 



To the same group belong two other species, M. angustidens 

 and M. Andium, and probably a third, M. Tapiro'ides, the 

 dentition of which is but imperfectly known. The molars of 

 the two first differ from those of %I. Ohioticus, in the same 

 manner that M. Arvernensis and M. Sivalensis differ from 

 M. latidens; viz. the crown ridges, instead of being trans- 

 verse, are composed of mammiUte, which are placed more or 

 less alternately, projecting into the interspaces and inter- 

 rupting thefr continuity. The teeth of M. Andium are re- 

 markable in being invested with a coat of cement, wliich fills 

 up the bottom of the hollows and is extended over the 

 mammiUse in a considerably greater quantity than occurs in 

 any other species of true Mastodon. These three species, 

 M. Ohiotims, M. angustidens, and M. Andium, constitiite a 



i 



