dr. falconer's arrangement. 139 



beginning • with the Elephantida?, through the Mastodon series to the'Dino- 

 theriuni ; at one end of the line are placed the very long thin plates of the 

 Elephas Priinigenius ; at the other, the gradually expanding cones of 

 the Mastodon Giganteus. While the Elephantine teeth generally affect the 

 laminated form, the Mastodon affect the conical. These forms, however, are 

 not always distinctly expressed on the external part of the tooth. Another 

 difference which may be considered general, though not without exceptions, 

 is the longitudinal furrow which divides the whole crown of the Mastodon 

 tooth into .two parts, and does not exist in the elephant. 



The Mastodons are separated into two groups ; one called Trilophodon, Trilophodon 



■ Group. 



and the other, not particularly named, which might be called Tetralophodon. 

 The Trilophodon group contains M. Giganteus, M. Angustidens, and M. 

 Andium. They ai'e distinguished by possessing three transverse ridges in 

 three of their teeth, viz. the third, or last deciduous molar ; the fourth, or 

 first permanent or antepenultimate molar ; and the fifth, or second perma- 

 nent or penultimate molar. 



In the other group there are also three species, viz. M. Latidens, Tetralopho- 

 don Group. 



M. Arvernensis, and M. Sivalensis. This group is distinguished by the 

 possession of four ridges in each of the three teeth above named, hence 

 called Tetralophodon. The Mastodon Arvernensis is said to have been 

 hitherto confounded with Mastodon Angustidens ; but, according to Dr. 

 Falconer, it* has uniformly four ridges in the teeth alluded to, while the 

 Angustidens has three, only. 



Having laid down the distinctive characters of the groups, we look next 

 for differences between each of the species which constitute these groups. 

 In the Trilophodon group the M. Giganteus is readily distinguished from 

 M. Angustidens and M. Andium by the absence of papilhe — the small 



