FREE INSTITUTE OF SCIENCE 



29 



MASTODON 



feebly developed. The outer lobes are conical and are medially extended by 

 an offset, which is variably prominent and divided into tubercular eminences, 

 and is separated by a notch from the contiguous inner lobe. 



At the front of the crown a stout tubercular process springs from the 

 basal ridge and appears like an extension of the anterior buttress of the inner 

 lobe in advance of the position of the outer lobe. At the back of the crown 

 is a similar process divided into tubercular eminences, more medial in position 

 and disconnected from the inner lobe. The basal ridge is well developed 

 internally, and is thickest where it embraces the first inner lobe, continuous 

 forward and outward. Internally it is thin, interrupted at the base of the 

 middle lobe, and produced into conspicuous eminences at the entrance of the 

 valleys. A considerable quantity of irregular cementum occupies the bottom 

 of the principal valleys and other recesses of the crown. 



The measurements of the tooth are as follows : 



Fore and aft diameter of the crown . • 

 Transverse diameter at fore part 

 Transverse diameter at back part 

 Height at anterior-internal lobe, obliquely , 

 Height at posterior-internal lobe, obliquely . 



122 mm. 

 75 " 



Plate ii. fig. 4 represents the first true molar contained in the right jaw 

 fragment. The tooth is entire, but worn to such an extent that all the con- 

 stituent lobes display considerable dentinal areas. The crown conforms in 

 structure with that of the second molar above described. The exposed 

 dentinal areas are concave, while their enamel borders are convex. Those of 

 the first and second inner lobes are the broadest, and are quadrilobate, with 

 the inner division much the larger. That of the third inner lobe has nearly 

 half the outline of the former. The dentinal areas of the outer lobes, much 

 the smaller, are transversely elliptical. 



The basal ridge is well produced internally, but only in slight eminences 

 at the entrances of the valleys externally. In front of the crown it exhibits 

 the same conspicuous eminence as in the posterior molars, continuous with 

 the anterior buttress of the inner lobe, and extending in advance of the con- 

 tiguous outer lobe. At the back of the crown is a conspicuous pyramidal 

 eminence springing from the basal ridge, and most prominent opposite the 

 middle of the inner lobe. 



The measurements of the tooth are as follows : 



