DAKOTA AND NEBRASKA. 245 



fossil, but on inquiry ascertained that the collection was dispersed, and the tooth had 

 disappeared. Dr. Hays joined in the search and shared with me the disappointment 

 I experienced, as he had known the tooth." 



The cast, represented in figure 13, plate XXVII, is that of a last inferior molar of 

 the left side, and indicates the tooth to have been intermediate in character with the 

 corresponding teeth of M. americanus and M. angustideiis. Fore and aft it is about 

 the size of small specimens of teeth of the former species, but is proportionately 

 narrower, and agrees better in this respect with those of the latter species. 



The crown presents four divisions or ridges and a heel, each of the former being 

 composed in the usual manner of a transverse pair of lobes. The anterior two ridges 

 are considerably worn, and the first one is broken away at its fore part. They bear 

 some resemblance to those of the Tambla tooth, and the neighboring transverse valleys 

 are obstructed at the middle in the same manner. Likewise the anterior two inner 

 lobes, from trituration, have exposed trefoil tracts of dentine. The third ridge of the 

 crown is but slightly worn, and, though constructed on the same plan as those in 

 advance, exhibits the distinctive features more clearly. The outer lobe appears to be 

 composed of a connate pair of lobules, of which the included one is much the smaller, 

 and has springing from it in advance and occupying the second valley of the crown 

 a large mammillary eminence. The corresponding inner lobe exhibits a pair of fore 

 and aft prominent buttresses obstructing the transverse valleys, and in addition an 

 offset connate with the included lobule of the outer lobe. The fourth division of the 

 crown is less well-developed than those in advance, which are of nearly uniform size. 

 Its lobes ai'e each composed of a distinct pair of lobules, of which the included ones are 

 smaller, contiguous, and situated somewhat in advance of the exterior lobules, so that 

 they contribute to obstruct the middle of the third transverse valley of the tooth. 

 The heel of the crown is composed of a pair of small mammillary eminences, a 

 rudiment of an additional ridge to the tooth. 



The fore and aft diameter of the cast in its present condition is sixty-eight lines, 

 and when perfect is estimated to have been about six and one-third inches. Its width 

 at the base of the second ridge of the crown is thirty-two lines. The height of the 

 third nearly unworn ridge is twenty-five lines from the base of the crown ; that of the 

 fourth ridge twenty-two lines. 



The cast exhibits so remarkable a resemblance in every respect with the repre- 

 sentation of a tooth described by Prof. Owen in his History of British Fossil 

 Mammalia, that it might readily be taken for a copy of the latter tooth. This is 

 described, on page 280, as a penultimate upper molar of Mastodon angustidetis, from 

 the fluvio-marine crag of Norfolk, England, and is represented in figure 98. On com- 

 paring the latter with our representation of the cast, figure 13, plate XXYII, one 

 cannot fail to be struck with the apparently accidental resemblance of the specimens 



