434 Professor 0. C. Marsh— The Skull of Protoceras. 



bones. The gigantic Brontotheridse of the Lower Miocene all hacT 

 prominent horn-cores on the maxillary bones, somewhat like those 

 of the male Protoceras. One of the most unexpected examples, 

 however, in this order, appears in the Miocene genus Diceratheriitm. 

 This animal, although a true rhinoceros, had a pair of horn-cores on 

 the nasal bones, while all other rhinoceroses, living and extinct, are 



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Fig. 1 . — Cranium of Dinoceras mirabUe, Marsh. Type ; seen from the side. 

 One-seventh natural size. Middle Eocene : "Wyoming Territory, U.S.A. 



either without horns or have them on the median line. In short, 

 horns in pairs are unknown in existing mammals, except in the 

 artiodactyles, an order of later development, but now the dominant 

 group of ungulate mammals. 



The Shull of the Male. 



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

 characters above mentioned, has others of equal interest, if not of 

 still greater taxonomio value. The general appearance of the 

 adult male skull is well shown in Plate XIX, accompanying the 

 present article. 



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 Protoceratidte. 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 long flexible nose, if not 



