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



more forward. A still longer interval separates the first and 

 second lower premolars, the latter beginning the continuous molar 

 series. The second premolar has the crown much compressed, 

 while the third and fourth are triangular in form. The three true 

 molars have the usual crescents corresponding to those above, but 

 no inner cingulum. 



The Cranium of the Female. 



The type-species of the genus Protoceras, as already stated, was 

 the skull of a female, and it may be well to repeat here its essential 

 features as given in the original description already cited. In 

 Fig. 2 below, most of the main characters of this type-specimen are 

 represented. 



" In general form and proportions, this skull is of the ruminant 

 type. Its most striking feature is a pair of small horn-cores, 

 situated, not on the frontals, but on the parietals, immediately 

 behind the frontal suture. These prominences were thus placed 

 directly over the cerebral hemispheres of the brain. 



" Tlie 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. 



Fig. 2. — Cranium of Protoceras celer. Marsh ; seen from above. One-half natural 

 size, a, depression in maxillary ; /, frontal ; h, horn-core ; o, orhit ; p, parietal ; 

 s, suture between frontal and parietal. Miocene : South Dakota. 



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

 two deep grooves leading backward to the supra-orbital foramina. 

 Behind these, half-way to the hoi-n-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. 



