RHINOCEROS OF NEBRASKA. 555 
posterior valley. Its principal valley is intruded upon only by a slight bulge at 
the middle of the antero-internal lobe. 
In the corresponding lobe to the latter in the preceding two molars, the bulging 
posteriorly successively increases, and also exists anteriorly. This dilatation of the 
antero-internal lobes decreases the depth externally of the anterior valleys, so that 
they slope downwards from their entrance, and in the trituration of the teeth they 
are obliterated from without inwards, leaving no islets of enamel behind as in the 
premolars. 
In the specimen under consideration, the abrasion of the first true molar has 
effaced the outer half of the anterior valley. 
In the second to the fourth premolars inclusive, the inner lobes are confluent 
internally at their bases, but to a less extent in the anterior than the remaining 
two of those designated. From trituration, the latter in the specimen exhibit the 
remains of the anterior valleys as simple trilateral pits of enamel occupying the 
centre of a broad space of dentine, while in the former the anterior valley still con- 
tinues open internally. The posterior valleys of the posterior three premolars are 
as deep externally as the corresponding portion of the anterior valleys. The basal 
ridge of the three teeth just designated, envelopes the base of the postero-internal 
lobes to a much greater extent than upon the preceding lobes, and in the specimen 
under observation the first premolar presents an almost equilateral triangular tritu- 
rating surface, possessing both internal lobes in a rudimentary state. Constituent 
portions of the basal ridge connect the bases of the lobes together. The short ante- 
rior valley remains open internally, but the external extremity only of the posterior 
exists as a small trilateral pit of enamel. 
Inferior molars.—(Tab. ix., fig. 2.) The teeth preserved in the fragments of 
lower jaws referred to belong all to the posterior four molars, and these do not differ 
in their form from those corresponding to them in recent species of Rhinoceros. 
A basal ridge exists in all, but is obsolete on the inner side of the posterior three 
molars and the outside of the hinder lobe of the same teeth, except the last. 
ADMEASUREMENTS. 
Inches. 
Length from occipital condyle to first premolar, . : ; 143 
Distance from end of post-glenoid tubercle to parietal crest, : é 6 
Height of face from alveolar border to supra-orbitar sisson : ‘i 5% 
Distance from occipital condyle to anterior margin of orbit, ‘ ‘ 103 
Breadth of skull at zygoma, . : : 82 
‘¢ of forehead at ork ostitie’ estdbetanten, : : : 7 
: ’ 7t 
Length of upper molar series, 
