97 



reduced condition continues interruptedly on the inner and outer parts. In 

 "outline the base of the crown is ovoidal, with the narrower extremity corre- 

 sponding with the outer part of the anterior lobe. The tooth is inserted by 

 a pair of fangs widely compressed, conical, and convergent internally. The 

 transverse diameter of the crown of the last upper molar is 20 lines ; its fore 

 and aft diameter is nearly 18 lines. Tlie description of the upper molars of 

 Dinoccras mirabilis, and the size of the last one, as given by Professor Marsh, 

 so well apply to the tooth above described as to lead me to suspect that the 

 animal so named is the same as Uintatherium rohustum. 



The fragments of both sides of the lower jaw of the latter, represented in 

 Fig. 11, Plate XXV, and Figs. 32, 33, Plate XXVII, contain the last molar tooth, 

 also represented in Figs. 9, 10, of the former plate, and Fig. 31 of the latter. 

 The tooth has an oblong square crown, rounded at the corners and moderately 

 constricted at the middle laterally. It is inserted in the jaw by a pair of 

 wide, compressed conical fangs. 



The crown is composed of three lobes, with oblique intervening valleys, 

 which receive the pair of lobes of the corresponding upper tooth when closed 

 upon the lower one. 



The anterior lobe forms nearly half the crown, and rises internally in a 

 point, which is the most prominent part of the tooth. The front and back 

 surfaces are sloping, and the former is transversely concave, and bounded by 

 a short, oblique basal ridge. The inner and outer surfaces of the extremities 

 are convex, and extend to the bottom of the crown. The acute summit 

 curves downward and outwai'd from the inner point. It is worn off on the 

 posterior slope with a more forward direction externally, and exhibits a nar- 

 row tract of exposed dentine. The prominent point of the inner extremity 

 is notched just below the summit postero-internally. 



The posterior and middle lobes of the crown are nearly of the same size 

 and prominence. The posterior lobe is separated from the anterior lobe 

 internally by a deep, angular notch, and diverges from it externally. It 

 forms the posterior convex surface of the crown, and has an anterior sloping 

 surface defined from it by a ridge curving from the inner side backward and 

 outward, and then becoming continuous, with a basal ridge sweeping down- 

 ward to the bottom of the middle lobe of the crown externally. The middle 

 lobe appears like an ovoidal wedge introduced from the outer side, and sepa- 

 rating the anterior and posterior lobes. Its summit is worn off with a slight 



posterior slope, and exhibits an exposed tract of dentine. 

 13g 



