TITANOTHERIUM. 77 



(XVII. 2) presents a basal ridge, descending at its anterior and posterior margin to 

 the masticating surface ; but it does not possess a median salient ridge like that of 

 Palaeoiherium, nor does it present the anterior characteristic fold of the Rhinoceros. 

 The portion of this surface corresponding to the posterior lobe inclines inward, in 

 its course downward, and the anterior portion of the same surface rises into a 

 median longitudinal prominence, descending to the apex of the anterior lobe. 



The inner side (1) of the teeth is transversely convex, and forms a thick and 

 deep cingulum, with a wide, obtusely rounded border, enveloping the bases of the 

 inner lobes. 



The latter, of which that anterior is very much the larger, are confluent their 

 entire height, and are isolated from the outer lobes nearly to their base ; thus de- 

 stroying the principal transverse valley as it usually exists in the molars of Rhi- 

 noceros and Palaeoiherium, and creating one antero-posteriorly (3, 4). 



The antero-posterior valley, at the position corresponding to the d&pressed in- 

 terval of the outer lobes, communicates with a large and deep trilateral pit, homo- 

 logous with the termination of the principal transverse valley in the molar teeth of 

 Rhinoceros, and with a similar pit in the teeth of Palaeoiherium. Posteriorly this 

 valley is connected with another, but smaller and shallower pit, which also finds 

 its homologue in the Rhinoceros and Palaeoiherium. In one of the specimens (4), 

 probably the third premolar, the antero-internal lobe is more confluent with the 

 corresponding outer lobe than in the other; and its internal cingulum is more 

 irregular. 



In the trituration to Avhich these teeth have been subjected, the enamel has been 

 worn off from the masticating surface of the outer lobes, very nearly to the base 

 of those within, leaving a broad tract of exposed dentine, which is bilobed inter- 

 nally by the deep central enamel pit. In the supposed third premolar (4), this 

 tract is continuous, anteriorly upon the summit of the antero-internal lobe, but in 

 the fourth premolar, the summits of the inner lobes present a separate antero-pos- 

 terior tract. 



The enamel of these teeth, except where worn, is slightly rugose, and, upon the 

 outer lobes, externally exhibits numerous transverse undulating lines. It is thickest 

 upon the inner lobes, where it is one line and a half; and upon the external part 

 of the outer lobes it is about one line in thickness. 



The measurements of the two specimens, in their present condition, are as 

 follows : — 



Inches. Lines. 

 Antero-posterior diameter of third premolar .....•" o 



Transverse diameter of third premolar ....■•• 1 -l" 

 Antero-posterior diameter of fourth premolar ....•• ^ ' 



Transverse diameter of fourth premolar ....... 1 ^ 



One of the fragments of the premolars above mentioned, exhibits the inner lobes 

 entirely associated as one, and disconnected to their base from the outer lobes. This 

 connate lobe has the form resulting from the confluence of an anterior larger cone, 

 with another posterior and smaller (7). The sides of the connate lobe, where not 

 affected by attrition, are rugose, and the summit presents a clavate tract of dentine 

 with a border of enamel nearly one line and a half in thickness. 

 11 



