414 THE NATUEAL HISTORY REVIEW. 



Unicorn Javan species. The third collis is notched and cusp- 

 less in R. Javanus, and R. bicornis of Sennaar : all of which are 

 points of agreement. In the Sumatran species, on the other 

 hand, the third Collis bears a cusp, as in the tichorhine 

 Bhinoceros. 



3. The guard. The B. unicornis of India, B. Javanus, B. 

 bicornis and B. Sumatranus, bear a strongly defined guard on 

 their anterior aspect as in the megarhine species. 



4. The external lamina. In the four last-named species, as in 

 the megarhine, the second costa of the external lamina, in R. 

 simus on the other hand and B. tichorhinus the first, is the 

 higher. 



In fine, the dentition of the megarhine species presents a com- 

 bination of characters now scattered among widely-isolated species 

 of the same genus. The curious problem as to how the characters 

 of the extinct became shared among the living species, and how 

 others, not found in the former, were superinduced in the latter, is, 

 to my mind at least, incapable of any other solution than that 

 offered by Mr. Charles Darwin's " Theory of descent with modifica- 

 tion." The unicorn B. Javanus, and the bicorn B. Sumatranus 

 approach more closely to the extinct bicorn B. megarhinus than any 

 other living species. 



LIST OF WOODCUTS. 



rig. 1. Left upper milk molar 1, crown surface, \. 



2. „ „ external surface, \. 



3. Left upper milk molars 2, 3, 4, crown surface, ^. 



4. Upper milk molar 4, crown surface, ^. 



5. Left upper milk molars, 2, 3, 4, external lamina, ^. 



6. Right lower milk molar 1, inner surface, nat. size. 



7. Right lower milk molars 2, 3, 4, inner sm-face, 5. 



8. „ „ external surface, |. 



9. Right upper molar series, except Premolar one, crown surface, \. 



10. Right upper molar two, crown surface, nat. size. 



11. „ external lamina, nat. size. 



12. Left lower premolar one, inner surface, nat. size. 



13. „ „ external surface, nat. size. 



14. Right lower molar, series, except premolar one, inner surface, 5. 



15. Right lower molar two, external surface, nat. size. 



