Marsh — Principal Characters of the Protoceratidce. 167 



The Male Skull 



The skull of the male Protoceras, in addition to the marked 

 characters above mentioned, has others of equal interest, if 

 not of still greater taxonomic value.* The general appearance 

 of the adult male skull is well shown in Plate II, accompany- 

 ing the present article, and the special anatomical characters 

 are represented more clearly in the different views on Plates 

 III, IY, V, and VI. 



Figure 2. — Skull of Colonoceras agrestis, Marsh; type, with brain cast; seen from 

 above. About one-half natural size. Eocene. 



Figure 3. — Skull of Dicer atherium advenum, Marsh; type, with brain cast ; seen 

 from above. One-sixth natural size. Miocene. 



Aside from the various horn- cores and protuberances upon 

 the skull, the next most notable feature is the very large, open 

 nasal cavity, a character which pertains to both sexes, and to 

 the entire family of the Protoceratidw. This peculiar feature 

 is of even more importance than the horn-cores, judging from 

 its functional significance, and its rarity in more recent forms 

 of artiodactyles. It indicates clearly in the living animal a 



* Osborn and Wortman, Bulletin, Amer. Mus. Nat. Hist., vol. iv, p. 351, 1892. 

 See also Scott, Jour. Morph., vol. xi, p. 303, 1895. 



