PETERSON: THE AMERICAN DICERATHERES. 425 



Type.SkuW of young male. C. M., No. 1,271. 



Horizon. — Miocene . 



Locality. — Agate Spring Fossil Quarries (Quarry A.) Sioux County, Nebraska. 



Paratype. — Posterior portion of skull from same quarry as the type. Ver- 

 tebrae and limb-bones referred to same species. 



Specific Characters. — Premaxillary somewhat reduced in length. Grinding 

 surface of cheek-teeth comparatively simple. Nasals long in front of the horn cores 

 especially in females. Muzzle long. Border of anterior nares comparatively little 

 extended backward. Skull quite saddle-shaped, especially in males, due to the develop- 

 ment of the horn-cores and the high inion. Postorhital ridges less oblique than in the 

 John Day forms due to the enlargement of the brain-case. A sagittal crest present; 

 this is proportionally long, but not especially strong. Zygomatic arches somewhat 

 more expanded posteriorly and the basi-cranium shorter than in earlier John Day 

 forms. Paroccipital and postglenoid processes sometimes touching one another at 

 their bases so as to enclose the external auditory meatus. Lower jaws heavy and the 

 angle little or not at all everted. Animal smaller than D. armatum of the John Day 



formation. 



General Description. 



Since the earlier descriptions of this species the type has been restudied. 

 Illustrations, which in some respects are more accurate than those which appeared 

 earlier, are also herewith presented. I, furthermore, add data recently obtained, 

 and have corrected certain errors, which occurred in earlier publications. 



In Science (I.e.) it was stated that the nasals were found in the talus below the 

 point where the skull was taken out. The nasals were separated from the skull at 

 the fronto-nasal suture, but agree with the skull found in situ, with the correspond- 

 ing parts missing. I at once associated the difTerent parts as those of one indi- 

 vidual, and have not since found any reason for changing my mind. Confirming 

 my view, a good skull of this species in Dr. Loomis ' collection at Amherst has the 

 fronto-nasal suture quite open, as in the type. Dr. Loomis assures me that the 

 nasals belong with the skull of his specimen, which is of approximately the same 

 age as the type. (See Fig. 13.) 



In the original description it was said that the brain-case is large, while Loomis 

 states that the brain-case is comparatively small, a statement which only holds 

 good so far as the present species and D. cooki are concerned. From the earlier 

 John Day forms D. niobrarense may be distinguished by its having the brain- 

 cavity of larger size. I stated that there is a well-formed sagittal crest, but I did 

 not especially emphasize the fact that the crest is strong. From the Amherst 



