312 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 8, 



inferior incisors, were several years afterwards advanced by Prof. 

 Owen (who must obviously have overlooked the previous remarks of 

 Bronn) in his 'British Fossil Mammalia*' as being distinctive of 

 Mastodon from Elephant in a well-marked and unequivocal manner. 

 But they are assuredly neither absolute nor constant, whether regarded 

 in a positive or negative view, as generic distinctions. For on the one 

 hand, premolars have not yet been met with in M. (Trilophodon) 

 Ohioticus, in place in the jaws, although made a subject of special re- 

 search by Dr. Warren, Dr. Jackson, and myself, upon a large quan- 

 tity of materials t, up to a very late date ; nor have they been yet 

 met with in certain species of the Tetralophodon group ; while, so 

 far from being restricted to species of Mastodon, they have been de- 

 tected by us in a typical fossil Elephant from India, E. (Loxodon) 

 flanifrons, both in the upper and lower jaws, in as great a number 

 as in any known Mastodon. And as regards inferior tusks, although 

 these have been observed in three species of the Trilophodon group, 

 and in two of Tetralophodon, there are other species in which, among 

 abundant materials, they have not been noticed up to the present 

 time, even in young individuals, where they might have been with 

 most confidence looked for. This remark applies with especial force 

 to the forms here called M. {Trilophodon) Hwnboldtii, and to M. 

 (Tetralophodon) Sivalensis and M, (Tetralophodon^ Arvernensis. 



Swayed by considerations of this nature, and struck more parti- 

 cularly 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 in- 

 ferior incisors, De Blainville % 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 andikTa^- 

 todontes, MxAtx the common designation of '* Elephas." This pro- 

 posal has deservedly met with little favour among palaeontologists 

 and zoologists. 



There are characters however, which, when once recognized, are 

 happily of an obvious and readily applicable nature to distinguish 

 Mastodon from Elephant, and which further enable the palaeontolo- 

 gist 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 ordi- 

 narily present six molar teeth from first to last, in the order of hori- 

 zontal 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- and first or antepenultimate true-molar, but in addition 



* Brit. Foss. Mam. p. 274. f Warren, On Mastodon giganteus, p. 80. 



X De Blainville, Osteographie : Des Elephants. 



