Marsh — Principal Characters of the Protoceratidce. 173 



"The frontal bones are very, rugose on their upper surface, 

 and this rugosity extends backward on the parietals, and to 

 the summit of the horn-cores, as well as between the latter, 

 and along the wide sagittal crest. The horn-cores are well 

 separated from each other, and point upward, outward, and 

 backward, overhanging somewhat the temporal fossae. They 

 are conical in form, with obtuse summits. 



" Between the orbits, the frontals are depressed, and marked 

 by two deep grooves leading backward to the supra-orbital 

 foramina. Behind these, halfway to the horn-cores, is a 

 median prominence resembling in shape the corresponding 

 elevation on the skull of the male giraffe. The brain cavity 

 is unusually large for a Miocene mammal. The occiput is 

 very narrow, indicating a small cerebellum, and the occipital 

 crest is weak. The occipital surface slopes backward. 





Figure 6. — Back of female skull of Protoceras celer ; type ; seen from above. 

 Figure 7. — Front of same skull ; seen from below. 



Both figures are one-half natural size. Miocene. 

 /frontal; h, horn-core; m, first molar; n, posterior nares; o, orbit; p, 

 parietal ; pm, second premolar ; s, suture between frontal and parietal. 



"The facial region of the skull is narrow and elongate, On 

 the outer surface of the maxillary, just above the antorbital 

 foramen, there is a deep depression, which probably contained 

 a gland. The usual ruminant fossa in front of the orbit 

 appears to be wanting. The orbit is large, and completely 

 closed behind by a strong bar of bone. 



