FREE INSTITUTE OF SCIENCE 



MASTODON 



floridamcs are constructed on the same pattern. They possess three fangs ; 

 and the crown, which is nearly a third wider fore and aft than transversely, is 

 composed of three pairs of transversely-united conical lobes, springing from 

 a broad base and separated by deep angular valleys, which accommodate the 

 summits of the lobes of the opposed teeth. The summits together of each 

 pair of lobes form a crest, with a wide and variably deep notch terminating in 

 a median vertical cleft which defines the inner from the outer lobe. The bor- 

 der of the crest is subdivided usually into five or six mammillary eminences. 

 The inner and outer lobes conjoin by medial offsets, mostly distinct, and they 

 are characteristically different. 



The inner lobes have comparatively small medial offsets, sometimes 

 scarcely developed or obsolete, and usually producing at the summit but a 

 single eminence, contiguous to the main one. Fore and aft they expand in 

 stout buttresses, of which those contiguous unite and divide the intermediate 

 valleys across their middle for more than half their depth. Inwardly the but- 

 tresses are defined by deep furrows from the main body of the lobes. Their 

 free border extends from the summit of the lobes in rows of mammillary 

 eminences. The anterior buttress of the first inner lobe is extended by an 

 equally stout ridge in advance of the position of the contiguous outer lobe. 

 In the third inner lobe the posterior buttress is feebly produced or is altogether 

 absent. 



In the outer lobes the medial offsets, defined by variably strong furrows 

 fore and aft, are nearly as large as the main portion of the lobes, and at the 

 summit are usually divided into a pair of eminences, and not unfrequently 

 more. Rudiments of buttresses, corresponding with those of the inner lobes, 

 appear as variable tubercles in the intermediate valleys, springing from the 

 medial offsets. 



At the back of the crown is a wide, flattened, pyramidal talon, springing 

 from or embraced by the adjacent basal ridge, and variably divided into a row 

 of unequal nipple-shaped eminences, of which the larger are mostly inward. 



A variable tubercular basal ridge embraces the crown. Thickest in front 

 of the latter at its inner half, it is usually next best developed along the inner 

 side of the crown, forming conspicuous eminences at the entrance of the 

 valleys. Externally it is less marked and often obsolete, except as variably 

 developed eminences at the entrance of the valleys. It sometimes also 

 appears more or less distinct from the talon of the crown. 



In the wear to which the upper molars are subjected, the inner lobes sue- 



