DAKOTA AND NEBRASKA. 43 



Wolf, has an elongated conical crown, obtuse in front, subacute behind, and with a 

 posterior mammillary basal heel. 



The third upper premolar has the crown shorter and broader than the second, with 

 nearly the same form, but provided with a better developed basal heel posteriorly. 

 It bears a resemblance to the corresponding tooth of the Hysena, but is not so long 

 nor so robust in the proportions of its principal cusp. 



The inferior premolars, four in number, except the first pair are closer together 

 than the corresponding teeth of the Wolf, 



The first lower premolar is lost in the fossils of Hycenodon horridus. The remain- 

 ing premolars successively increase in size. 



The second premolar has a conical crown, with the base considerably extended 

 behind, and with the anterior border shorter than the posterior border, which is 

 concave. 



The third and fourth premolars have strong conical crowns, obtuse anteriorly, sub- 

 acute posteriorly ; and are provided posteriorly with a stout basal heel, which is 

 subtrenchant at the extremity. These teeth resemble the corresponding ones of the 

 Hyaena, but are proportionately less robust. 



The superior true molars, three in number, consist of a smaller anterior pair and a 

 large sectorial tooth. 



The first upper true molar has its crown longer and thicker, but not so broad as 

 that of the last premolar in advance. Externally it resembles the latter tooth in 

 form, except that its basal heel is extended obliquely downward and has a subacute 

 border. Internally it further differs in possessing a strong median extension of the 

 base, which is supported by a third fang. A feeble basal ridge extends interruptedly 

 along the inner part of the crown. 



The second upper true molar, smaller than the tooth in advance or behind, appears 

 apparently unnatural in position. Its crown is thickest anteriorly, and there appears 

 to be supported by a pair of connate fangs, while it narrows posteriorly and is there 

 sustained by a single fang. The inner surface of the crown forms an inclined plane. 

 Viewed externally the crown appears as a modified form of that of the preceding 

 tooth, with the principal cusp much reduced and the basal heel in a proportionate 

 degree expanded into a wing-like lobe with a wide inferior trenchant edge. The 

 summit of the principal cusp is slightly cleft. At the bottom of the crown ante- 

 riorly there is a transverse basal ridge. 



The upper sectorial molar, the last of the true molars and the largest of the series, 

 is a powerful and formidable looking weapon, well adapted to the penetration and 

 cutting of all kinds of animal food, including bones. It is implanted by three fangs 

 in the ordinary mode of the superior sectorial molars of ordinary carnivora. The 

 crown is longer in proportion to its breadth than in the Wolf, Cat or Hyaena. It is 



