os) 
JTITANOTHERIUM. Wi 
The triturating summits of the lobes present more or less broad crescentic sur- 
faces of exposed dentine, bordered by enamel, with the horns rising to the inner 
side of the teeth, and there becoming confluent and forming simple conoidal promi- 
nences. The enamel spaces embraced by the horns of the crescentic summits of 
the lobes do not slope towards the base of the teeth internally, as is represented to 
be the case in the figures of the corresponding teeth of Palaeotherium, but they form 
deltoidal concavities, which are nearly on the same level with the dentinal cres- 
cents, and are bounded internally by a thick obtuse border; open, however, at the 
middle to the bottom of the concavities. 
The third lobe of the last molar is smaller than those in advance, and resembles 
one of them atrophied at its posterior half. The external basal ridge of this tooth 
ceases upon the third lobe just before reaching its posterior surface; but upon this 
internally a small portion is developed. 
The enamel of the teeth is rugose, and is most so externally, in which position 
it also presents a very uniform series of transverse striae. At the triturating sur- 
face of the teeth externally, where the enamel is thickest, it measures one line and 
two thirds. 
The measurements of the teeth in the fragments of jaw just described, are as 
follows :— 
ANTERO-POSTERIOR. TRANSVERSE. 
Inches. Lines. Inches. Lines. 
Last molar : . ; 3 ; : : 3 ian 4 6 1 10 
Second true molar 3 2, 
8 1 
bo Co 
First true molar j : : 
10 
In the collection of Dr. Owen, there is preserved a portion of the left side of a 
lower jaw (PL. XVI, Figs. 2, 5) containing true molars exactly like those just de- 
scribed, and the fangs of the preceding two premolars. Accompanying this specimen, 
and probably derived from the same individual skeleton, there are also the crown of 
the second or third left lower premolar, the crown of a lower canine, and fragments 
of two upper molars. The fragment of lower jaw, before it became infiltrated with 
mineral matter, was very much crushed, and at present it is more light and friable 
than any other of the specimens of fossils which have been brought from Nebraska. 
It is considerably smaller than the corresponding part of the bone in Dr. Prout’s 
specimens, measuring nine and a half inches along the series of true molars, five 
and a quarter inches in depth below the last molar, and an inch and a quarter in 
thickness below the first true molar. Two inches posterior to the last molar it is 
seven and a quarter inches in depth. Its form closely corresponds with that of 
Dr. Prout’s specimens, as does also the form of the teeth contained in it, except 
that their basal ridge is not of uniform depth, but gradually rises in a pyramidal 
manner, and becomes thinner from between the lobes to their most prominent ex- 
ternal part. 
The teeth are more worn than in the specimens of Dr. Prout, and their enamel 
presents the same appearance, but in the same position is a third of a line less in 
thickness. 
The measurements of the true molars are as follows :— 
