338 RIIIXOCEROS. 



emarginated behind, and it repeats, but with reduced dimen- 

 sions, the usual posterior fossette of the penultimate m. 2 of 

 Fig. 1, Plate XVI. The form of this fossette is exhibited by 

 fio-s. 3 and 4, h, and its relation to the other parts by the ex- 

 ternal view, fig'. 5, h, of Plate XVII., where a shallow and in- 

 distinctly defined channel, bounded on either side by a ridge, 

 is continued upwards upon the enamel-surface from the basal 

 fossette to the apex of the crown, but becoming more and 

 more indistinct as it ascends. This channel is the homologue 

 of the posterior fissure (Oss. Foss., Rhin., Plate VI. fig. 4) in 

 the last molar of Rhin. ticlwrhinus and Rhin. simus. On the 

 opposite side of the same figure (fig. 5, i) a vertical groove is 

 seen descending from the anterior outer notch. In the last 

 molar of Rhin. hicomis (Plate XVIII. fig. 7), the small 

 tubercle (h) is the abortive representation of the rim of the 

 posterior fissure of fig. 3, h, of Plate XVII. 



In consequence of the basal position of the cup of the 

 posterior fissure in the last molar of Rhin. hemitoschus, the 

 abrasion of the crown cannot reach it so as to form an 

 insulated fossette till the last stage of use, and ordinarily it is 

 enwrapped by the very thick layer of cement, so as to be 

 only indicated by a protuberant gibbosity, as is seen in m. 3 

 of fig. 2, Plate XVI., and less distinctly in m. 3 of fig. 1 of 

 the same Plate. The channel, which is continued upwards 

 from the cup, remains usually inconspicuous. 



The last true molar, therefore, in the Gower species exhi- 

 bits the remarkable combination of the following characters : 

 namely, a triangular crown with a V-shaj>ed summit, and 

 two fossettes ; one corresponding to the middle vallej r , the 

 other to the posterior fissure ; the posterior barrel narrow 

 and compressed, and giving off a double crochet. In its sys- 

 tematic relations it occupies an intermediate position between 

 Rhin. hicomis and Rhin. ticlwrhinus. 



In the description of all the molars, reference has been 

 made to the thick layer of cement. This dental constituent 

 is present in greater or less quantity on the teeth of all the 

 species of Rhinoceros. But in Rhin. hemiicechus the mass of 

 the layer is so great as to become a character of specific 

 importance. The proportion which it bears to the shell of 

 enamel is best seen on the anterior barrel of m. 2 of fig. 1, 

 Plate XVII. It is there partly denuded, and the enamel 

 looks as if set in a casing of cement. In Fig. 2, Plate XVI., 

 all the molars are completely enveloped by an enormous coat 

 of cement, through which the edging of enamel protrudes. 

 It is also most abundant in all the molars of Fig. 1, Plate 

 XVI. In the last true molar of Fig. 2, Plate XVI., the 

 cement is seen to form a thick layer, insinuated between the 



