236 Bulletin American Museum of Natural History. [Vol. XIII, 



The most primitive species of American Rhinoceros, Trigonias 

 osborni, recently described by Lucas, presents an entirely differ- 

 ent type of cutting teeth from that seen in R. gaudiyi. 



Superior Molars of Diceratheriin^. 



In London, in Paris, and in Munich are numbers of small ex- 

 tremely primitive molar and premolar teeth from the Middle and 

 Lower Oligocene Phosphorites of Mouillac, Quercy, and Bach, 

 also from the Lignites of Cadibona, which are for the most part 

 erroneously catalogued as D. minutum and its synonym, D. 

 croizeti, specific names ivhich tvere applied originally to much more 

 highly evolved Upper Oligocene types. In point of evolution all 

 these upper grinding teeth resemble the Lower Oligocene Dicer- 

 athere types of America, especially such species as CcBnopus {Ac- 

 eratherium) copei ; but, as in the case of the lower jaws (of ^. 

 gaudryi and R. velatmum) above described, it is not possible to 

 determine their phyletic relations or exact systematic position at 



Fig. 5. Dicerathcrium jninnium. Type: Paris. Fourth premolar, first and second 

 molars. X \- After Cuvier. 



present. It is probable that all these teeth belong either to R. 

 velaunum, R. gaudryi, or some allied species. (See Fig. 4.) 



Characters. — Dentition: premolars unlike molars; premolars 2-4 with 

 proto- and metalophs confluent upon wear ; a crista in premolars 3-4 ; milk pre- 

 molars dp^-dp* with complete crests resembling the molars ; molars with rudi- 

 mentary antecrochet (jirotoconule fold) ; more or less marked external cingulum, 

 rudimentary metaconule fold ; variable cingulum suggesting a ' cingule ' at 

 entrance of median valley (Fig. 4). 



London, British Museum Collection : No. M. 1732, superior molars i and 2, 

 Loc, Phosphorites, Bach, Lalbenque (Lot), France (see Fig. 17, Lydekker, 



