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27 

 MASTODON 



tubercles or sublobes. Internally considerable tubercles, as isolated elements 

 of the basal ridge, occupy the entrance of the valleys. The fore part of the 

 basal ridge appears remarkably worn from pressure of the tooth in advance. 

 A small quantity of cementum occupies the bottom of the valleys and the 

 deeper depressions of the surface of the tooth. 



The measurements of the teeth arc as follows : 



Fore and aft diameter of the crown . . . . 91 mm. 



Transverse diameter of the crown in front . . . 45 " 



Transverse diameter of the crown behind . . . . 52 " 



Height of crown obliquely at the third outer lobe . . 51 " 



Height of crown obliquely at the third inner lobe . . 44 " 



Plate ii. fig. i represents the triturating surface of the crown of a much 

 worn lower first true molar of the left side. The tooth nearly accords in con- 

 stitution with the former, but is somewhat wider transversely, and elements of 

 the basal ridge are not so conspicuous internally. The distinction between 

 the anterior lobes has been destroyed by wear, and the enamelled structure at 

 the front of the crown has entirely disappeared. On the second pair of lobes 

 the dentinal tracts arc united by a small isthmus, but on the posterior pair 

 they are still separated by a double boundary of enamel. Dentinal islets have 

 "also appeared on the basal tubercles at the back of the crown. 



The measurements of the tooth arc as follows : 



Fore and aft diameter of the crown ..... 80 mm. 

 Transverse diameter of the crown behind . . . 57 " 



Two specimens from the bone-bed of Mixon's plantation in the collection 

 of 1890 consist of the front and back portions of the crowns of the last lower 

 molars, apparently from the same individual, but different from the former. 

 Represented in plate iii. fig. 4 and plate v. fig. i, they serve to give the char- 

 acter of the entire tooth. Like the other specimens of last molars described, 

 the present one had nearly assumed its functional position, as from use at 

 the fore part the summits of the anterior two pairs of lobes are but slightly 

 abraded. The tooth is most like the corresponding ones last described, but is 

 still narrower in its proportions. The medial offsets of the outer lobes are less 

 developed, while those of the inner lobes are better developed and more 

 distinct. The basal ridge is completely absent, both externally and internally. 

 A considerable quantity of cementum occupies the recesses of the crown. 



The measurements of the tooth are as follows : 



