GENERIC DISTINCTIONS OF PROBOSCIDEA. 7 



present time, even in young 1 individuals, where they might 

 have been with most confidence looked for. This remark 

 applies with especial force to the forms here called M. (Trilo- 

 pJiodon) ttimboldtii, and to M. (Tetralophodon) Sivalensis and 

 M. (Tetralophodon) Arvemensis. 



Swayed by considerations of this nature, and struck more 

 particularly with the identity of general characters and close 

 similarity of form running throughout the whole of the 

 osteology of the species of Mastodon and Elephant, with the 

 exception of the molars and inferior incisors, De Blainville 1 

 abandoned the idea of there being any sufficient generic 

 difference between the two, and made a retrograde step, 

 arranging all the forms in two divisions, Lamellidontes and 

 Mastodontes, under the common designation of ' Elephas.' 

 This proposal has deservedly met with little favour among 

 palaeontologists and zoologists. 



There are characters however, which, when once recog- 

 nized, are happily of an obvious and readily applicable nature, 

 to distinguish Mastodon from Elephant, and which further 

 enable the palaeontologist to break up an unwieldy mass of 

 species into subgeneric groups, that are at the same time 

 natural and convenient. Putting aside for the moment, as 

 extraneous, the consideration of incisors and premolars, and, 

 as in the case of Dinotherium, taking the milk and permanent 

 dentition together, the species of both Mastodon and Elephant 

 ordinarily present six molar teeth from first to last, in the 

 order of horizontal succession — i.e., three deciduous or milk 

 molars, and three true molars. It was stated above, that in 

 the Dinotherium the last milk molar and the antepenultimate 

 or first true molar are invariably characterized by a ternary- 

 ridged formula, or, in other words, that their crowns are 

 divided into three ridges. Applying this criterion in a similar 

 manner to Mastodon, we have found, that not only the last 

 milk molar and first or antepenultimate true molar, but in 

 addition the second or penultimate true molar, being three 

 teeth in immediate contiguity, in all the species (with one re- 

 markable exception) are severally characterized in both jaws 

 by an isomerous division of the crown into either 3 or 4 ridges. 

 These three isomerous-ridged teeth may, for convenience of 

 description, be referred to in the aggregate as 'the inter- 

 mediate molars,' a term which has been applied to them from 

 their position by Fischer and by Laurillard. 2 To the species 

 which present the ternary-ridged formula we have assigned 

 the subgeneric name of Trilophodon ; 3 and to the quaternary- 



, ' De Blainville, Osteographie : Des I Naturelle, torn. viii. p. 29. 

 Elephants. ! 3 From rpus and \6<pos, three-ridged. 



2 Dictionnaire Universel d'Histoire 



