70 TITANOTIIEllIUM. 



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 Palaeo- 

 iherium. It inclines and terminates below as in the latter, but relatively is only 

 slit^htly concave, and it possesses no bounding salient ridge at its anterior part, 

 such as is represented in the figures of the teeth of Palaeoiherium in the works of 

 Cuvier, Jaeger, De Blaiuville, Gervais, and others. In the place of such a ridge, 

 the tooth forms a prominent convex margin, projecting, as in ruminants, in Rhinoceros 

 and PaJueotherium 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-iuternal loLc to that externally of the 



antero-external lobe .......... 1 6 



Height of latter from base to point. ........ 2 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 Palaeoiherium magniim, 

 are yet sufficiently different to indicate 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 Palaeoiherium, 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 TifanotJierium Proulii. 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 PalaeotJierium. 



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. 



