RHINOCEROS LEPTORHINUS. 375 



Dimensions. 



Extreme length of crown, outer surface 



Ditto, inner side ........ 1'85 



Transverse diameter in front, at base of enamel . 



Ditto ditto, behind 



Height of crown anteriorly, outer surface 



Ditto ditto, inner 



From these dimensions it is seen to be larger than the R. hemitcechus 

 tooth, and less advanced in wear. In this respect it closely resembles 

 De Christol's figure of R. megarhinus. 



Compared with R. hemitcechus there are the following differences : — 

 The crochet forms a very open angle with the posterior colline ; it is 

 longer and narrows towards the point. The termination of the valley 

 throws out from the outer ridge a thick combing plate, which is di- 

 rected at right angles to the crochet, and divides the cul de sac into 

 two compartments, as in the milk molar in Ponzi's collection. The 

 posterior colline is directed backwards, and has the peculiar torsion 

 shown in De Christol's figure. Further, the anterior overlapping sinus is 

 much more pronounced, and the anterior outer vertical groove is wider 

 and deeper. The enamel is smooth, with some cement on the outer 

 side, but the greater part is removed. There are some denticles in the 

 bottom of the valley, but these have been broken in picking out the 

 matrix of gravel. 



This tooth agrees in every respect with R. megarliinus, and proves 

 that species to exist in Italy. It has no inside bourrelet, nor inter- 

 columnar tubercle. 



There is another specimen (No. 112) also from Monte Sacro, in the 

 Mineralogical Gallery of the Museum, of the last successional premolar, 

 left side, beautifully preserved (PI. XXXII. fig. 5), and very little 

 worn (like No. 111). It shows a double crochet plate projected in 

 front and. downwards, as in De Christol's drawing (fig. 25 1 ), but is per- 

 fectly free from the combing plate of the outer ridge shown in that 

 figure. It is very nearly in the same stage of wear, and has plenty of 

 cement on the outer surface ; the crown is high. There is a well- 

 marked basal bourrelet on the inner side, proving it to be a premolar, 

 and a layer of cement above the bourrelet. The second and lower 

 crochet plate is much smaller than the upper ; the two are very unequal, 

 and it is also much less worn. There is very little obliquity in the 

 disc of the posterior barrel, which is parallel to the front barrel ; the 

 posterior valley is very large. Ponzi's worn specimen is proved by 

 this to be the third. 



Dimensions. — Length of crown, outer side, 175 in. Length of crown, inner side, 

 at base, 1-55 in. Length of ditto at middle, 1-55 in. Transverse diameter at base 

 anteriorly, 22 in. Transverse ditto posteriorly, 2-15 in. 



Lastly, No. 113, also from Monte Sacro, is a first true molar, upper 

 jaw, left side. The crown is nearly in the same stage of wear as 

 Ponzi's milk molar (PI. XXXII. fig. 7), but is a good deal rolled. The 

 posterior colline is broken off. 



1 Reproduced in PI. xviii. fig. 1 of this work. See antca, p. 328, note. — [Ed.] 



