FREE INSTITUTE OF SCIENCE 

 MASTODON 



the lower teeth, the lateral surface is more defined from those fore and aft 

 than in the others by variably prominent borders, which seem to correspond 

 with the more medial buttresses of the latter. A similar but feebler ridge is 

 not unfrequent in front and behind the medial offset of the same lobes. 



Ordinarily the crown of the last molar of the American Mastodon is 

 composed of four pairs of lobes like those of the molars in advance, with a 

 fifth pair variably developed or more or less rudimental, and rarely absent. 

 Commonly the anterior two or three pairs of lobes are nearly equal, while the 

 others are successively reduced. In the various specimens observed the 

 inner lobes of the upper and outer lobes of the lower molars have their 

 buttresses variably produced ; sometimes narrow and simple, at others thicker 

 and rugose, and again they may be so stout as to approximate the condition 

 in Mastodon cordillfriim. The medial offsets of the lobes are variably distinct 

 and tuberculate. The fifth pair of lobes, smaller than the preceding, are 

 exceedingly variable. Usually they appear as a pair of large but unequal 

 conical eminences, simple or subdivided transversely, or fore and aft ; some- 

 times there is but a single one and rarely none. 



The condition of the enamel in M. amcricanus is very variable. Mostly 

 on the lateral surfaces of the crown it is comparatively even, but striated 

 or finely wrinkled transversely. In the valleys usually it is less even, often is 

 more or less rugose, and not unfrequently is more or less coarsely wrinkled 

 longitudinally, and this condition in a variable degree may extend laterally. 

 The chief differences observed in the teeth of M. floridaiius from those of 

 M. americaiuis consist in the rather more conical than pyramidal form of the 

 constituent lobes of the crown, but especially in the great proportionate 

 development of the fore and aft buttress-like ridges of the outer lobes of 

 the lower teeth, and of the inner lobes of the upper teeth. In the valleys 

 crossing the crown, in the former, the contiguous buttresses conjoin and 

 obstruct their course for more than half their depth in the unworn teeth, 

 whereas in M. antericanus they scarcely interrupt them. The foremost buttress 

 at the front of the crown, from the summit of the lobe to which it pertains, 

 curves in advance of the contiguous lobe as a conspicuous tubercular ridge 

 united with the basal ridge. At the back of the crown a buttress is unde- 

 veloped and is substituted in the first and second true molars by a conspicuous 

 pyramidal and strongly tubercular production of the basal ridge. Further, 

 the intermediate extensions in the pairs of lobes are in general more distinct 

 as portions of these, and are more tubercular than in M. americaints. Ac- 



