RHINOCEROS LEPTORHINUS. 373 



(fig. 122), which has been worn down to about the same 

 degree, it will be seen that, in fig. 141, the valley, #, 

 is wider at its commencement, and that the termination, 

 where the letter is placed, is smaller and of a triangular 



Fig. 141. 



5th upper molar, Rh. leptorliinus. Nat. size. Clacton. 



form : in the tichorhine molar it is much more expanded 

 and bilobed by its extension towards the middle of the 

 outer surface of the crown. The valley between these 

 two terminal divisions, in the tichorhine molar, is so 

 shallow, that the outer lobe is soon separated as an island 

 of enamel, according to the pattern shown in fig. 126, 

 and the valley then preserves an almost uniform width 

 to the termination marked by the letter b. In the upper 

 molar of the leptorhine Rhinoceros, the valley is either 

 divided by the wearing away of the shallow fold of ena- 

 mel between the end of the narrow process entering the 

 valley and the opposite bank, e, whereby the end of 

 the valley, b, is wholly insulated, which change is shown 

 in the molar of the Rhinoceros leptorMnus, from Crozes, 



