FREE INSTITUTE OF SCIENCE 

 MASTODON 



37 



The measurements of the tooth are as follows : 



Diameter fore and aft of the crown ..... 126 mm. 

 Diameter transversely at base of the anterior lobes . . 64 " 

 Diameter transversely at base of the posterior lobes . . 78 " 



The crown of the right last lower molar tooth, represented in plate vi. fig. 

 I, is complete except that it is injured on the summits of the second pair of 

 constituent lobes. It is longer fore and aft, narrower transversely, and of 

 more uniform breadth in this direction than that of the upper molars. It is 

 slightly bent in the length, with the convexity inward and a less degree of 

 concavity outward. Like the upper molars, it is composed of four pairs of 

 lobes, springing from a broad base and with a larger talon, assuming more 

 the appearance of an additional pair of reduced lobes. The inner lobes are of 

 less transverse breadth than their homologues, the outer ones of the upper 

 teeth, due mainly to reduction in the medial offsets, which in this tooth exhibit 

 but a single eminence at the summit, instead of a pair as in the upper teeth. 

 The outer lobes are almost identical with their homologues of the latter, but 

 the posterior buttresses of the posterior pair are better developed. The inner 

 lobes are flattened internally, and the corresponding lateral faces are more 

 abruptly defined from those in front and behind than in the upper molars. 

 This condition of the inner lobes gives the inner surface of the crown a 

 flattened appearance not present in the corresponding or outer surface of the 

 upper molars. The outer lobes are almost identical with their homologues of 

 the latter, but in the third and fourth the posterior buttresses are better 

 developed. 



From the talon springs a pair of conical eminences, much larger than 

 those in the accompanying upper molar, and bounded behind by a strong 

 tuberous base. The pair of eminences are about half the size of the lobes in 

 advance, and are related to them as a fifth reduced pair. A strong basal ridge 

 extends from the front of the crown along the outer side to the talon, but 

 interrupted or thinning away at the base of the first outer lobe. 



The measurements of the tooth are as follows : 



Diameter fore and aft of the crown ..... 225 mm. 



Transverse diameter at base of first pair of lobes 



Transverse diameter at base of second pair of lobes 



Transverse diameter at base of third pair of lobes 



Transverse diameter at base of fourth pair of lobes . . 84 



Height of first external lobe .... 



