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 PI. xvi. fig. 5, and PI. xviii. 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, in 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,' pi. iii. 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. 



t See Dr. Grant in 'Proceedings of the Geological Society,' June 15th, 1842. 



