FOSSILS FEOM PERBI ISLAND. 405 



9*2 inclies in tlie former, while it is but 6*9 in tlie latter, and 

 at the back of the third tooth or first true molar, 8*7 inches 

 to 6*2 inches. The Perim fossil exhibits a like excess of 

 dimensions in relative thickness, the jaw measuring 5*1 

 inches in diameter under the second premolar, and 6*4 inches 

 at the middle of the penultimate molar, while in the European 

 species the corresponding dimensions are respectively 4 and 

 5 inches. In consequence of this great depth and thickness, 

 the jaw of the Indian fossil approaches very closely the 

 massive and turgid form seen in the typical Mastodons, such 

 as the M. giganteus ; while that of the European Dinotherium 

 is comparatively much thinner and more compressed. The 

 inner side of tlae jaw in the latter is very flat, differing in 

 this respect widely from the Mastodons generally ; in the 

 Perim fossil this flatness is much less, not exceeding that of 

 the Mastodon giganteus, and, behind, the body of the jaw 

 bulges out on either side, so as to yield nearly a circular 

 outline in section, and exactly to represent the form in the 

 American Mastodon. This resemblance is so great, that in 

 the absence of the crowns of the teeth, and from its huge 

 proportions, the fossil, when presented to the Museum and 

 up to this time, has always been regarded as the jaw of a 

 Mastodon. The relationship indicated by the shape of the 

 jaw is further borne out by the form and structiu-e of the 

 penultimate lower tooth, as described in the preceding part 

 of this paper. The enamel, which is thinner in the D. gigan- 

 teum, is as thick in the Indian species as in the lower 

 penultimate of the American Mastodon ; the outline of the 

 ivory ridge beneath the enamel is the same in both; the 

 crown ridges have the same transverse, continuovis, crenu- 

 lated, and trenchant form ; and what is most important and 

 significant of all, the hind talon, in respect of form, amount 

 of development, and the characteristic erenulation of its 

 edge, is so precisely similar, that this part in the one exactly 

 represents the corresponding part of the same tooth in the 

 other. The same direction of afiinity is further indicated 

 by the nearly horizontal line of protrusion and horizontal 

 plane of wear in the teeth, by the form of the ramus, coronoid 

 process, and angle of the jaw, and by the absence of antero- 

 posterior curvature in the outline of its lower surface, in all 

 of which particulars the American Mastodon deviates widely 

 from its congeners, and from the Elephantine t3rpe generally, 

 and approximates towards the Dinotherium. This tendency 

 is also shown in the very reduced formula of the teeth-ridges, 

 in the deflexion of the symphysis, its thick blufi" termination, 

 and in the inferior tusks. I shall soon have occasion in 

 another place to follow this subject at greater length, and in 



