14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6l 



the rostral portion beyond the molars, and the great downward curva- 

 ture of the narrow nasals. The tooth foldings are fully as compli- 

 cated, the teeth having besides the three fossettes occasionally another 

 accessory one on the inner border of the third upper premolar. The 

 dental formula is the same as in Ceratotheriuui, but the teeth are much 

 narrower and smaller generally and do not show evidence of much 

 cement in their composition. Another important skull difference is 

 the union of the post-glenoid and post-tympanic processes to form 

 a closed meatus. A further difference is found in the occipital con- 

 dyles which are widely separated at their bases. 



Thomas has proposed that C. si inns be included in this genus ' 

 because of the similarity in shape of skull and dental structure. The 

 great differences in the nasal region and the auditory meatus, how- 

 ever, are of too much weight to permit such grouping. 



The only living Asiatic rhinoceros which is related to the African 

 species is the two-horned Sumatra species, Dicerorhinus sumatrcnsis. 

 The skull of Dicerorhinus differs chiefly in the presence of functional 

 canines, but these show a strong tendency to reduction, the central 

 lower ones being absent and the lateral ones showing a tendency to 

 atrophy. The cheek teeth are much less specialized, being brachyo- 

 dont without complicated enamel folds. The skull is scarcely dolicho- 

 cephalic, showing much less occipital projection than Ceratothcrium. 

 In the structure of the auditory meatus and in the general shape of 

 the skull this genus approaches closely Ceratotheriiim. Its chief 

 differences are the presence of a pair of upper incisors and lower 

 canines, the lower incisors being absent. The shape of the nasals, 

 which are slender and pointed, however, is of less systematic sig- 

 nificance. 



The genus Rhinoceros, of which the great Indian one-horned 

 species, Rhinoceros unicornis, is the type, differs more widely in skull 

 characters than Dicerorhinus. In this genus the front teeth show 

 much less reduction, the lower canines especially being of large size, 

 and the middle upper incisors are present though of little functional 

 importance. The skull is brachycephalic, the occipital projections not 

 extending beyond the condyles, and in general shape it is much more 

 like that of Dicer os. The general shape and expansion of the nasal 

 bones is also much more like the condition we find in Diceros and 

 Ceratothcrium. The closed auditory meatus is one of the chief char- 

 acters which separates it from the other living genera. 



The trunk skeletal differences between Ceratothcrium and Diceros 

 are really wide, and serve only to accentuate the generic distinctness 



