MASTODON ANGUSTIDENS. 28] 
the size of the tooth, which is six inches in length, shows 
it to be the last but one in the molar series; and the 
convex bend of the grinding surface in the longitudinal 
direction, proves it to have come from the upper jaw. 
The work of mastication first impresses the fore part 
of the grinding surface, and the inner tubercles in the 
upper molars are always worn lower than the outer ones, 
By these marks, a Mastodon’s grinder may be readily 
referred to the jaw and the side of the jaw from which 
it originally came,—the tooth in question being the penul- 
timate grinder of the right side of the upper jaw. It 
must have belonged to a Mastodon that perished in the 
vigour of youth, before the attainment of full maturity ; 
for the two hinder pairs of tubercles had not been used 
in mastication: and it could not, therefore, have been 
shed in the ordinary course of dental change, since the 
last molar tooth must still have been concealed in its 
alveolar nidus of growth. 
The mutilated molar tooth of the Mastodon angustidens, 
represented in figure 99, was likewise obtained by Mr. 
Fig. 99. 
Penultimate lower molar, Mastodon angustidens, Fluyio-marine Crag, Norwich, 
1 ¢ ITA 
3 hat. size. 
Robert Fitch, F.G.S., ‘‘ from a crag-pit in the immediate 
vicinity of Norwich.” It is the penultimate molar of the 
left side of the lower Jaw, and had done good service to 
