MASTODON ANGUSTIDENS. 287 
pair of mastoid tubercles acquire their normal proportions, 
and the posterior ridge is developed into a group of tu- 
bercles ; in the large-sized variety, like that exemplified 
in the old male Mastodon angustidens, figured by Dr. 
Kaup in his Pl. xvi. fig. 5, and Pl. xvii. fig. 9, the tuber- 
cular talon assumes the character of a sixth pair of mastoid 
eminences, succeeded by a small tubercular ridge. (See 
figs. 96 and 97.) 
Analogous varieties of form and size are manifested by 
the last molar tooth of the Mastodon giganteus. In the 
Mastodon angustidens the larger and more complex ex- 
amples have been supposed to indicate a distinct species ;* 
in the Mastodon giganteus the varieties have been seized 
upon as characters, not only of distinct species, but of 
distinct genera.f The utmost signification that, m my 
opinion, can be legitimately assigned to them as distinctive 
characters, is in relation to difference of sex. 
Having thus briefly pointed out the principal characters 
of each of the seven molars of the Mastodon angustidens, 
I may add that those of the lower jaw are narrower than 
those of the upper; and that the upper molar teeth are 
characterised by the slight convex curve, described by the 
grinding surface in its longitudinal direction, and the lower 
molars by the corresponding concavity of the same surface. 
The fore part of an unworn molar is the broadest, and this 
part of the grinding surface shows first and most the effects 
of mastication; in the upper molars the inner range of 
tubercles are most worn, in the lower molars the outer 
range. By these characters a detached grinder of the Mas- 
in the ‘ Divers Mastodontes,’ pl. ili. fig. 4, exemplifies this variety ; and the form 
of the symphysis shows the specimen to have belonged to a female Mastodon. 
* See Dr. Kaup’s characters of Mastodon longirostris, * Description d’Ossements 
Fossiles de Darmstadt,’ cap. iv. 1835. 
+ See Dr. Grant in ‘ Proceedings of the Geological Society,’ June 15th, 1842. 
