RHINOCEROS IIEMITCECHUS. 341 



is present alike in the upper and lower molars in very great 

 thickness. 



Another character, equally obvious, is the very consider- 

 able amount of concavity in the common grinding surface of 

 the teeth, in the antero-posterior direction, from the ante- 

 penultimate premolar to the last true molar. This concavity 

 is much more pronounced than in the jaw of either B. tichor- 

 hinus or B. megarhinus, with which I have compared it ; and 

 that it is constant in B. hemitoechus is proved by its uniformity 

 in the three jaws having teeth in different stages of wear. 



Premolars. — The premolars agree very closely in form with 

 those of B. megarhinus, the principal difference being in the 

 proportion which their aggregate length bears to that of the 

 true molars. The antepenultimate (p.m. 2 of PI. XIX.), in 

 horizontal section, is somewhat wedge-shaped, contracting 

 from behind forwards to a narrow edge, which is bent in- 

 wards. Its outer surface shows the vertical groove of divi- 

 sion between the two crescents, and on the inner side behind 

 there is a well-marked niche indicating the concavity of the 

 posterior crescent. In B. megarhinus, the antepenultimate 

 in the same stage of wear is free from any corresponding 

 indentation. The anterior edge in the Gower specimen 

 forms a convex projection. The tooth agrees in the closest 

 manner with the Clacton tooth figured in the ' British Fossil 

 Mammalia,' Cut 136, p. 863, and there referred to B. leptor- 

 hinus. In the ' Bacon Hole ' specimen (fig. 1, PI. XXI.) 

 the antepenultimate premolar repeats the form presented by 

 p.m. 2 of PI. XIX. 



The penultimate (p.m. 3 of PI. XIX.) has the crown ground 

 down to a common sinuous disc. The indentation between 

 the two crescents forms on the outer surface a deep niche 

 directed forwards. The remains of the hollows of the crescents 

 on the inner side show that they were deep and boldly de- 

 fined. The crown of this tooth in B. hemitoechus is consider- 

 ably smaller, both in the actual dimensions and relatively to 

 the last premolar, than in B. megarhinus {vide Gervais, 

 ' Paleontologie Francaise' (PI. II. fig. 8). 



The last premolar (p.m. 4 PL XIX.) presents an oblong 

 crown, with two boldly pronounced crescents, which are 

 nearly of equal size. It is also very much larger in all its 

 proportions than the tooth which precedes it. Compared 

 with the corresponding premolar of B. megarhinus, the 

 following points of difference are observable : — 



1st. That the crown is much longer in relation to the 

 antepenultimate, and shorter in relation to the first true 

 molar, than in B. megarhinus. 



2nd. That the anterior horn of the front crescent is much 



