364 RHINOCEROS. 



penultimate grinder is in place, the sockets of the ante- 

 penultimate molar, and of the three adjoining premolars, 

 vacant ; that of the first premolar is obliterated : the whole 

 of the socket of the second, and part of that of the third 

 premolar are in advance of the back part of the symphysis. 

 Besides this well-marked distinctive character, the present 

 fossil displays the more convex curvature of the lower 

 border of the jaw, its greater thickness in proportion to its 

 depth below the premolar series. These differences are 

 well brought out in contrast with the portion of jaw from 

 the fresh- water beds of the Oromer Cliff, which belonged to 

 a younger individual, and of which comparative admeasure- 

 ments are subjoined: 



Rh. leptorhinus. Rh. tichorhinus. 



In. Lin. In. Lin. 



Depth of jaw below the middle of third premolar 20 30 



Greatest thickness of the same part of the jaw 17 18 



Depth of the jaw below middle of the penultimate molar 30 35 



Antero-posterior breadth of penultimate molar 20 19 



of last molar . 23 18 



The last two admeasurements show the characteristic 

 superior size of the molar teeth in the Rh. leptorhinus. 



Dr. Kaup has described and figured a portion of a lower 

 jaw of a Rhinoceros discovered in the Rhine formations 

 (" im Rheine gefunden"), the left ramus of which, according 

 to the figure,* contains the fourth, fifth, and sixth molars, 

 the roots of the third and second, and the anterior root 

 of the seventh molar ; the second molar being in advance 

 of the posterior commencement of the symphysis, as in 

 the lower jaw of the Rhinoceros leptorhinus of Italy, figured 

 by Cuvier (loc. cit. Rh. pi. ix., fig. 9), and as in the 

 specimen from Clacton, figs. 132 and 133. 



Dr. Kaup, believing that in his Rhenish specimen the 

 * 'Akten der Urwelt,' tab. ii., fig. 1 , p. 6. 



