DAKOTA AND NEBRASKA. 197 



Behind the posterior lobes, the basal ridge extending from each side and meeting at 

 the middle, then appears to turn forward and double upon itself. 



The measurements of the specimen are as follow: antero-posterior diameter of last 

 superior molar, 8 lines; transver,se diameter, 7i lines; length or depth of crown, 

 4 lineg. 



An isolated upper true molar, apparently the first of the series, represented in 

 figures 24, 25, may belong to the same animal as the teeth just described, though it 

 appears hardly broad enough in its proportions, and its lobes appear to be too smooth. 

 Probably it may belong to the same species as the lower jaw fragments, to the 

 exclusion of the other specimens of upper molars above noticed, or it may have 

 belonged to a species distinct from either. 



The crown is more square than in the Peccary, or the transverse and antero-poste- 

 rior diameters are nearly equal, agreeing in this respect with that of the correspond- 

 ing teeth of the extinct Palceochcerus, Ghceropotamus, Hyotherium and Hyracotherium. 

 The tooth indeed bears considerable resemblance to an upper true molar of the latter 

 animal, both in form and construction, and is of more complex character than the 

 corresponding teeth in the former genera. A dentated or crimped basal ridge 

 encloses the crown except on the inner side, though even here a constituent element 

 of the ridge occupies the bottom of the interval of the inner pair of lobes. Of the 

 lobes of the crown the outer are the largest and most distinct, and they form four- 

 sided pyramids. The inner pair of lobes are conical, and complicated by confluence 

 with lobes intervening between them and the outer ones. The antero-median lobe 

 is as large as the contiguous inner one, and almost completely connate with it. The 

 postero-median lobe is larger than the contiguous inner one, or it appears to be a 

 larger sub-division of the latter, and separated from it by a narrow antero-posterior 

 groove. In front, this postero-median lobe joins a mammillary eminence at the 

 middle of the transverse valley of the crown, and behind is continuous with an 

 angular median prominence of the basal ridge. The sides of all the lobes of the 

 crown ai'e comparatively smooth or devoid of wrinkles. 



The measurements of the specimen are as follow: antero-posterior diameter, 6i 

 lines; transverse diameter, 6 lines; greatest depth of crown, 3 J lines. 



LEPTOCHCERUS. 



Leptochcerus spectabilis.. 



Among the specimens of i-ather uncertain reference noticed at the commencement 

 of the previous chapter, is a small alveolar fragment of a lower jaw containing the 

 first and second true molar teeth, discovered by Dr. Hayden in the Mauvaises Terres 

 of White River. 



