76 TITANOTHERIUM. 
surface of the antero-external lobe (Fig. 4) is preserved, and this does not conform 
to the characteristic appearance of the corresponding portion of the tooth of Palaco- 
therium. Jt inclines and terminates below as in the latter, but relatively is only 
slightly concave, and it possesses no bounding salient ridge at its anterior part, 
such as is represented in the figures of the teeth of Pulaeotherium in the works of 
Cuvier, Jaeger, De Blainville, Gervais, and others. In the place of such a ridge, 
the tooth forms a prominent convex margin, projecting, as in ruminants, in Rhinoceros 
and Palaeotherium itself, exterior to the position occupied by anterior molars, and 
the basal ridge winds around the prominent margin to the anterior part of the 
tooth, descending to its masticating surface, which it reaches, in the specimen, a 
half inch internal to the outer edge of the latter. 
The dimensions of the tooth, so far as they can be ascertained in its present con- 
dition, are as follows :— 
Inches. Lines. 
Distance from the apex of the antero-internal lobe to that externally of the 
antero-external lobe. é ; 5 5 ; 5 : : papel 
Height of latter from base to point. . : é : . 3 é pues 2 
The enamel of the specimen just described is smooth upon the masticating sur- 
face, and at the base of the antero-internal conical lobe is about one line in thick- 
ness. On the outer side of the antero-external lobe it is rugose, and at the external 
masticating margin of this is also about one line in thickness. In other positions 
it is thinner, especially where it invests the inner sides of the outer lobes, the 
bottom of the antero-posterior valley, and the deep pits. 
The various fragments of lower jaw and teeth above described, though exhibiting 
a very great resemblance to the corresponding parts of the Pulaeotherium magnum, 
are yet sufficiently different to imdicate they probably belong to a distinct but 
closely allied genus, for which the provisional name of Titanotherium is proposed. 
The most important differences, which have been presented, are the absence of a 
basal ride at the inner side of the inferior molars, and at the same side of the frag- 
ment of a superior true molar; the nearly uniform depth of the antero-posterior 
and transverse valleys in the upper true molars; and the absence of the salient 
ridge, characteristic of Pulacotherium, at the anterior margin of the antero-external 
lobe of the last superior molar. 
In the collection of Mr. Thaddeus A. Culbertson, there are the crowns, nearly 
whole, of two superior premolars (Pl. XVII, Figs. 1-4), and fragments of two 
others, which also probably belong to Titanotheriwm Proutii. These, I stated in a 
verbal communication to the Academy of Natural Sciences, probably belonged to 
a species of Rhinoceros, for which the name R. Americanus was proposed,’ but they 
certainly do not belong to this genus, though closely partaking in its characters 
those of Palaeotherium. 
The nearly perfect crowns of the superior premolars are quadrate, and are 
greater in their transverse diameter than antero-posteriorly. Their outer side 
= 
* Proc. Acad. Nat. Sci., VI., 2. 
