1895. J ^5') [Cope. 



molars. He remarks that these teeth differ so much from the first upper 

 molars of the M. rohustua, that it may be necessary to refer the M. harlanii 

 to a genus distinct from the latter, with Harlan's name Orycterotherium. 

 Since, however, the teeth in question are second molars, the difference is 

 not so conspicuous, and generic distinction is not indicated. 



The first superior molar is smaller than the others, is more strongly 

 curved, and the section is a wide oval, the inner side much less convex 

 than the external. The second molar is curved slightly backwards and 

 also outwards, and has a rather narrowly oval or subreniform section, 

 since there is a median groove on the inner side, which is more conspicu- 

 ous in one of the teeth referred to this position than in two others. The 

 anterior and posterior faces are regularly rounded, and show no traces 

 of angulation. The dentine is about equally thick all around. The grind- 

 ing surface is worn into two oblique surfaces ; the anterior longer and 

 steeper, for the first inferior molar; the posterior shorter, (or tlie anterior 

 face of the apex of the second lower molar. The teeth have very much 

 the form and size of that one described by Leidy as representing his 

 Megalonyx dissimilis, but the beveling of the grinding face, and the equal 

 thickness of the dentine on the inner side, show that the species, at least, 

 are distinct. 



The third superior molar is bilobed on the interior side, the posterior 

 lobe being rather narrow ; and the external outline is rather narrowly 

 rounded, and is not truncate. The posteroexternal face is shallowly 

 grooved and concave. The long axis is very oblique to that of the jaw. 

 This tooth in the AI robustvs has the posteroexternal face convex, and the 

 posterointernal lobe is not so narrow; the axis is very oblique. In the 

 M. renidem it is more different, having the section reniform with the long 

 axis nearly anteroposterior. The fourth superior molar has also a bilobate 

 outline on the internal side, the posterior lobe more produced than the 

 anteri.jr. The crown is quite narrow anteroposteriorly, and the external 

 outline is narrowly truncate. It is represented as rounded in the M. 

 robustus. It has a greater anteroposterior diameter in the J/, renidens, 

 and the anterior face is separated from the rounded posteroexternal by an 

 angle. In both of the North American species the groove of the interior 

 face is deeper than is represented to be the case in the M. robustus. The 

 last superior molar is much like that of M. robustus. 



The specific difference which distinguishes the M. harlanii most con- 

 spicuously from the AI. robustus is then the form of the second superior 

 molar. This tooth is much larger in the former, and has an elongate 

 subreniform section, while in the M. robustus the section is round. The 

 third and fourth superior molars also are rather narrower in anteropos- 

 terior diameter in the M. harlanii. 



It is unnecessary to describe the inferior molars, as this has been already 

 done by Leidy. The reseiublance to those of the 31. robustus is quite 

 close. 



