Cope.] 452 [Mays, 



As the skull belongs to an animal not quite adult, I describe tbe dental 

 characters from the second individual mentioned as having been sent from 

 the same locality in Oregon. In this one it is observable that the inner 

 edges of the cups of the incisors are well developed, but the latter are 

 only partly filled with cenientum. The fourth premolar is two-rooted and 

 is half overlapped by the third. The latter is of usual form, produced 

 anteriorly. The anterior inner crescent is distinct from the posterior 

 inner, but is narrowly connected with the anterior outer. The lakes have 

 a narrow communication. In the molars of typical form the posterior in- 

 ternal column is almost cut off from the adjacent crescent by the deep 

 posterior notch or loop, which also narrows the posterior crescent at this 

 point. The borders of the lakes are not much complicated in this speci- 

 men. They display on the third premolar only one well marked inflec- 

 tion on their adjacent faces, and two (one minute) on the posterior part 

 of the internal border in both. The posterior extremity of the posterior 

 internal crescent sends an angle inwards along the edge of the crown. 

 One or two loops point towards the internal column. 



In the Montana series, the premolars and first true molar of one side 

 are preserved, and two true molars of the opposite side. Their crowns are 

 less worn than those just described, and the enamel borders of the lakes 

 display more numerous inflections. Thus the anterior border of the pos- 

 terior lake has three deep inflections, while the adjacent boundary of the 

 anterior lake has but one ; this one however bounds a loop by nearly join- 

 ing another deep notch entering from the inner posterior direction. Then 

 there is a deep notch in each lake coming from the direction of the ante- 

 rior and posterior margins of the crown respectively. One loop extends 

 towards the inner column. 



In the Oregon skull, already mentioned, the superior molars display dif- 

 ferent degrees of wear in such a way as to be very instructive. The pre- 

 molars are least worn ; and in them we observe (1) that the posterior 

 internal column is distinct from the adjacent crescent like the anterior 

 one ; (2) that the mutual connections between the internal crescents are 

 very narrow ; and (3) that the inflections of the borders of the lakes are 

 few and shallow. In the second true molar, which is a little more worn, 

 there is one deep inflection on the adjacent border of each lake, of which 

 the anterior one nearly cuts off a loop by approaching a notch from the 

 inner side. In the first true molar, whicli is, of course, the most worn, 

 the posterior lake has the full number of three notches on its anterior 

 border. 



The masticating surface of the molars of this species is worn into trans- 

 verse angular grooves and ridges more distinctly than in any other species 

 of the genus. 



The cranium, already mentioned, is somewhat distorted by pressure, 

 but many characters are clear. The facial concavity is different from 

 that of H. specioimm in its greater size and more posterior extension, and 

 also in its expansion downwards to the maxillo-malar ridge, as in certain 



