TRANSACTIONS OF WAGNER 

 24 



MASTODON 



extends from the outer lobe to the base of the inner one, resembling the 

 extension of the anterior buttress of the first outer lobe in the lower back- 

 molars. Tubercular processes, elements of the basal ridge, occupy the en- 

 trance of the valleys of the crown. 



The transverse diameter of the crown at the middle pair of lobes is 48 mm. 



Plate iv. figs, i , 2,6, and 7 represents the first lower premolars of both 

 sides, and though apparently from the same individual present some differences. 



The left tooth, imperfect at the fore part and in the figure restored from 

 the other specimen, has a fore and aft irregular ovoidal crown, slightly con- 

 stricted at the middle and narrower in front. It is composed of four lobes, of 

 which the anterior, nearly equal, are the higher and of greater fore and aft 

 breadth, while the posterior are unequal, and together of greater width trans- 

 versely. The anterior lobes appear as laterally compressed cones, separated 

 by a deep groove behind, but scarcely distinct in front. Of the posterior 

 lobes, which are conical, the outer is nearly twice the size of the other, and in 

 the specimen its summit is worn so as to exhibit an exposed dentinal tract in 

 the form of the figure 8. At the back of the crown is a tritubercular heel in 

 which the inner tubercle is double the size of the outer ones. 



In the right tooth, at the base of the anterior lobes in front of the crown 

 is a ledge, an element of a basal ridge, which was apparently absent in the 

 former tooth. The postero-external lobe is much more worn, exhibiting a 

 broad dentinal area. The contiguous inner lobe of the left tooth in this one, 

 in which the part is imperfect, appears to have been substituted by a thick, 

 somewhat tubercular ridge, extending from the antero-internal lobe to the back 

 of the crown. The teeth have a pair of fore and aft connate fangs. 



Their measurements are as follows : 



Right tooth . Left tooth. 



Fore and aft diameter of the crown . . 28 mm. 28 mm. 



Transverse diameter of the crown in front . 15 " 14. 3 " 



Transverse diameter of the crown behind . 16.3" 17 " 



The first lower premolars described resemble the corresponding teeth of 

 Mastodon angustidens, but are considerably smaller and exhibit slight details 

 of difference. 



The crown of the first premolar has a prominent convex base, from which 

 project four unequal conical lobes, closely united, and together enclosing a 

 central pit. The constituent lobes may be viewed as having an arrangement 

 in transverse pairs, but from their less proportionate development the condition 



