TITANOTHEEIUM. 75 



tract of dentine (Fig. 5) extending to the broken margin of the tooth. The exter- 

 nal portion of the dentinal surface about its centre, and near the posterior margin, 

 is occupied by a pair of trilateral enamel islets, which are the remains of the termi- 

 nations of transverse valleys, such as exist in the molars of Bhinoceros and Palaeo- 

 tlierium. 



The fragment of a superior true molar (PI. XVI., Figs. 6, 7) presents a large 

 conical protuberance, corresponding to that antero-internal in the PalaeoiJierium 

 magnum. It has the enamel of its apex just worn through, leaving a discoidal 

 surface of dentine about one line in diameter. External to the conical lobe are 

 remains of the abraded masticating surface of the outer lobes of the tooth, and at the 

 base of the former, there exists one side (Fig. 7) of a deep pit homologous with that 

 at the base of the posterior half of the inner face of the antero-external lobe of the 

 corresponding tooth in Palaeotherium magnum. Antero-internally to the base of 

 the conical lobe, a thick, obtuse prominence (Figs. 6, 7) exists, which is a portion 

 of a basal ridge; but of this no trace exists on the inner side of the tooth, like that 

 in Palaeotherium magnum. 



In Dr. Owen's collection, there are also the isolated crowns of an inferior first 

 and last true molar (PI. XVII., Figs. 8-10), apparently from two other distinct 

 individuals of the same species as that indicated by the specimens just described. 



The measurements of these are as follows : — 



Antero-posterior diameter of tlie last inferior molar .... 

 Transverse diameter of the last inferior molar ..... 

 Antero-posterior diameter of the first true molar .... 



Transverse diameter of the first true molar ..... 



Inches. 



Lines. 



4 



3 



1 



7 



2 



10 



1 



10 



In the collection of Dr. Prout, and accompanying the two portions of a lower 

 jaw, which have been the subject of investigation, is a portion of the left superior 

 posterior molar, probably belonging to the same species, though not to the same 

 individual (PI. XVI., Figs. 4, 5). What is preserved of this specimen exhibits a 

 strong resemblance to the corresponding part of the homologous tooth in Palaeotlie- 

 rium magnum; but it presents several important differences. 



Upon the masticating surface of the crown, the valleys everywhere, antero-poste- 

 riorly as well as transversely, are nearly uniform in depth (Fig. 5). 



The summits of the outer lobes have been denuded of their enamel, and present 

 the remains of a broad W shaped tract of dentine, while the apex of the antero- 

 internal mammillary lobe has not yet had its enamel worn through. 



As in PalaeotJie7'ium magnum, at the base of the posterior half of the inner face 

 of the antero-external lobe, there is a deep elliptical pit of enamel, and a little pos- 

 terior to this is a second smaller and shallower pit. 



The external face of the crown of the superior molars of Palaeotlierium, as de- 

 scribed by Cuvier, inclines inward as it descends, and is divided by three longi- 

 tudinal salient ridges {arretes) into two concavities, rounded towards the fang, and 

 terminating in a triangular cusp at the triturating surface, the basal angles of 

 which rest upon the salient ridges. 



In the special subject under investigation, about three-fourths only of the outer 



