1 8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6l 



but differs widely in the brachycephalic skull and brachyodont cheek 

 teeth. The open character of the .meatus, which is characteristic of the 

 oldest genera, as well as the three living genera just mentioned, is not 

 found in any of the more recent fossil genera. These three living 

 genera are all two-horned forms. 



Most recent authors have associated Ceratotherium simum closely 

 with Coelodonta antiquitatis the woolly rhinoceros of northern 

 Europe and Asia. This course, however, does not seem justifiable, 

 considering the great differences in the rostral portion of the skulls. 

 In the woolly rhinoceros the whole anterior portion of the nasals, 

 premaxillse and maxillae is united into a solid mass by the thickened 

 osseous development of the mesethmoid. The vomer also shows a 

 tendency to become very thick and heavy. The resemblances are 

 mainly the dolichocephalic character of the skull and the structure 

 of the cheek teeth. 



Compared to Diceros, Ceratotherium shows much more speciali- 

 zation. The occipital projection of the skull is immensely greater, in 

 fact, it is the extreme reached by rhinoceroses, while Diceros is quite 

 at the other extreme in this regard, at least among recent species. 

 The cheek teeth &how the same extreme specialization over those of 

 Diceros and are at least as specialized, as in any other known genus ; 

 but dental differences of this sort are not of much phylogenetic impor- 

 tance, for some of the oldest forms exhibit much specialization of this 

 sort. In a measure, Ceratotherium shows more primitive skull char- 

 acters than fossil species, like Coelodonta antiquitatis, where there is 

 a great ossification of the internasals and a union of this bone with the 

 maxillae, intermaxillae and nasals into a solid rostrum. The open 

 auditory meatus is another primitive character which Ceratotherium 

 has retained. Coelodonta shows somewhat less occipital projection 

 and apparently less development of the cement layer in the cheek 

 teeth. In Ceratotherium the cement forms a thick layer and enters 

 largely into the structure of the teeth. 



There are no fossil forms known which show a really close affinity 

 to Ceratotherium. The genus may have been evolved in the Continent 

 which is still its home. If this has been the case we should not expect 

 to find any close allies in the later fossil forms of Europe and Asia, 

 unless migration has taken place. Notwithstanding the great differ- 

 ences in shape of skull and tooth structure separating this genus and 

 Diceros, there may be considerable geographical justification for the 

 combination of these two forms into a single genus as proposed by 



