

RHINOCEROS HEMITCECHUS. 339 



plates of the dcnible crocliet and lining the walls of the 

 valley. I have ascertained that it is equally abundant in 

 all the molars of this species from the caves of Oreston 

 and Durdham Down, and from the flnviatile deposits of 

 Clacton, and other similar localities. In the teeth of ex- 

 isting species, such as Rhin. bicornis and Rhin. simus, the 

 coat of cement cracks and dislaminates, by long exposure to 

 the weather. This accident will account for its absence in 

 certain teeth of Rhin. hemitozchns, in which the cement had 

 probably disappeared from weathering before they were em- 

 bedded in the matrix. When the matrix is a calcareous paste, 

 the layer of cement is apt to be detached from the enamel 

 along with it, as appears to have happened to the external 

 surface of the molars in the Bacon Hole specimen, figs. 1 

 and 2, Plate XVII. The shell of enamel is very much thinner, 

 in proportion to the other dental elements in this species, 

 than in Rhin. tichorhinus. In the latter the external surface 

 is very rugous, while in the former it is comparatively 

 smooth. The difference is so considerable that in many 

 instances the teeth of the two species can be distinguished 

 by this character alone. 



De Christol has directed attention to the fact, that in 

 genera of the same families, the older forms have a less 

 coating of cement on their teeth than the newer types. Thus, 

 in Hipparion, the layer is much thinner in proportion than 

 in species of the genus Equus, and in Aceratherium than in 

 Rhinoceros. The same difference applies to the Miocene 

 species of Rhinoceros as compared with the modern forms. 

 He has ingeniously attempted to give a general expression 

 to the observation, designating the older forms Acemento- 

 dontes, and the newer Gementodontes. Without accepting the 

 generalization as universally applicable, it is worthy of 

 remark that cement abounds on the teeth of Rhin. tichorhinus 

 and Rhin. simus, and in the extinct form Rhin. hemitcechus, 

 while it is comparatively scanty in the teeth of Rhin. mega- 

 rhinus and in specimens attributable to Rhin. leptorhinus. 



Inferior Molars. — The molars of the lower jaw, in all the 

 species of Rhinoceros, present fewer and less appreciable mo- 

 difications of the general form than the upper ; and they are 

 in consequence of less avail in the distinction of the species. 

 For this reason, they would 'have been described, on the present 

 occasion, with much more briefness than the upper, but for 

 the fact that the materials for instituting a comparison be- 

 tween R. leptorhinus and R. hemitcechus are much more abund- 

 ant, in the shape of lower jaws and teeth, than of tipper. 

 Cuvier, having omitted to pay sufficient attention to the cha- 

 racter of the upper molars in R . leptorhinus, during his journey 



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