50 E. L. Troxell — Ccenopus, the Ancestral Rhinoceros. 



Not only in size but in the general form of the skull 

 does this specimen resemble C. tridactylus; it has the ris- 

 ing and double parietal, ridges extending into the 

 sagittal crest. The nasal bones are long and slender, 



Fig. 6. — Diceratherium armatum Marsh, Holotype. Molar-premolar series. 

 X 1/3. (See Peterson 1920 for reproduction of complete skull.) 



slightly wide over P^, where there appear actual shoulders 

 or barbs resembling in this feature C. copei. Another 

 specimen in the collection, Cat. No. 12059, Y. P. M., has the 

 broad thick nasals, presumably of the male, but they do 

 not show the rising protuberances so typical of the later 

 Diceratherium. 



Measurements of New Subspeoies and also of D. armatum. 



C. C. C. C. D. 

 alius nanolophus metalophus avus armatum 



No. 12052 No. 12489 No. 10254 No. 10251 No. 10003 



Y.P.M. Y.P.M. Y.P.M. Y.P.M. Y. P. M. 



mm. mm. mm. mm. mm. 



Molar-premolar length . . . 205 194 254 



Premolar series, length... 98 98 98 111 129 



Molar series, length 115 102 139 



P*, width, base 37 39 39 50 



P*, length, center 27 28 26 34 



M^ width, ant 37 43 39 44 53 



M^, length, center 33 38 33 38 44 



M^, width, ant 39 48 40 45 56 



M^ length, center 38 41 35 39 50 



M", width, ant 43 39 50 



M^, length, inner side 39 35 48 



Summary. 

 With further study of the great family of rhinoceroses 

 it becomes evident that they can not be classified on the 

 presence or absence of horns, a sexual variation; the 

 female and young dicerathere had no horns; probably 

 the male acerathere had them, at first in an incipient 

 stage. 



^ The -g^enus Ccenopus Cope includes nearly a dozen dis- 

 tinct species and subspecies, representing a long line of 



