12 BRITISH AND EUROPEAN FOSSIL MASTODONS. 



inolars less in the adult state than M. (Triloph.) angustidens ; 

 nor have they been observed in M. {Triloph.) Humboldtii. 

 They occur probably in M. (Triloph.) Tapiro'ides. Their 

 presence or absence has not yet been ascertained in the other 

 species of Trilophodon. These teeth have been observed in 

 situ in the upper and lower jaws of M. (Tetraloph.) longiros- 

 tris, and in the upper o$M. (Tetraloph.) Arvernensis. They have 

 not yet been seen in situ in the other species of Tetralophodon. 

 Inferior incisors have been discovered in M. (Triloph.) angus- 

 tidens, M. (Triloph.) Ohioticus, and M. (Triloph.) Tapiro'ides; and 

 also inikf. (Tetraloph.) Andium and M. (Tetraloph.) longirostris, 

 in the first of which they occasionally attain a very large 

 size. They do not appear to occur ever in M. (Tetraloph.) 

 Sivalensis, nor in M. (Tetraloph.) Arvernensis. Their presence 

 or absence in the two other species of Tetralophodon has not 

 yet been satisfactorily determined. The ridge-formula, as 

 being respectively ternary in Trilophodon, and quaternary in 

 Tetralophodon, is very constant, the only doubtful case being 

 presented by the form or forms named Mastodon Andium by 

 the French palaeontologists. Cement, although quantita- 

 tively inconspicuous in most of the species of both subgenera, 

 is present in considerable abundance in the valleys of the 

 crowns of M. (Tetralophodon) Perimensis and in M. (Triloph.) 

 Humboldtii. In the former it fills up the bottom of the in- 

 terstices between the mammillae. The transverse or alternate 

 direction of the mammillae of the ridges, and the open or 

 interrupted nature of the valleys connected therewith, are 

 not equally defined in all the species, intermediate stages 

 being met with. But the ridges are invariably transverse 

 and the valleys open in M. (Triloph.) Borsoni, Ohioticus, and 

 Tapiro'ides, and in M. (Tetraloph.) latidens; while the mam- 

 millae are constantly more or less alternate, and the valleys 

 interrupted, among the Trilophodons in M. (Triloph.) angusti- 

 dens, Humboldtii, and Pandionis; and among the Tetralo- 

 phodons in M. (Tetraloph.) Sivalensis and Arvernensis. The 

 most complex crowns are presented in the Trilophodons by 

 M. (Triloph.) Pandionis (an Indian fossil species recently dis- 

 covered, and as yet undescribed) and M. (Triloph.) Hum- 

 boldtii, and among the Tetralophodons by M. (Tetraloph.) 

 Sivalensis and Arvernensis. The upper adult molars in several 

 of the species — e.g., M. (Triloph.) angustidens and M. (Tetra- 

 loph.) Andium — were invested with a longitudinal belt of 

 enamel, disposed more or less spirally, and reaching the apex. 

 The lower incisors, according to Lartet, are constantly devoid 

 of any such belt. In M. (Triloph.) angustidens inferior incisors 

 would appear to have been common to males and females, 

 and not to have been a mark merely of sexual difference. 



