PETERSON: THE AMERICAN DICERATHERES. 423 



determined from the type. It is, however, most probable that this tooth is wanting, 

 especially when we consider the proportionally small development of the premaxil- 

 lary in the type, which is apparently much lighter and is no doubt shorter than, 

 for instance, in Coenopus tridactylus of the upper Oligocene. The later geological 

 formation in which this new species was found is also to be considered. The 



Fig. 12. Diceratheriurn gregorii. No. 12933, Coll. Ainer. Museum. Top of cranium. X i 



nasals were apparently of considerable length in front of the very slight swelling 

 on the anterior portion of the nasals. The crushing of the anterior region of the 

 skull gives to the anterior nares an unusually low position, low even when proper 

 allowance is made for the distortion which has occurred. This may, or may not, 

 be a valid character. The postorbital ridges of the frontals converge very grad- 

 ually, somewhat as in the John Day form {D. annectens), but the brain-case is 

 somewhat larger in proportion. The sagittal crest is low, but well-defined, and 

 the inion is intermediate between the John Day form and D. niobrarense of the 

 Nebraska Miocene, that is to say, the rise from the sagittal crest proper to the 

 top of the inion is very much more gradual than in D. niobrarense, even when the 

 difference of sex and the crushing sustained by the specimen is taken into account, 

 thus more like what is seen in D. annectens, but the slight emargination on the 

 posterior face of the inion is more as it is in D. niobrarense. The inion itself is 

 less rugose and the lambdoidal crests are thinner than in D. annectens, which may 

 be a sexual character. The top of the skull when in perfect condition was on the 

 whole less saddle-shaped; the zygomatic arches lighter, less prominent posteriorly, 

 and united with the sides of the squamosals more obliquely than in D. cooki. The 

 postglenoid and paroccipital processes are in touch with one another, but are 

 not so completely fused as in the latter species. The external ear is large and in 

 shape more nearly as in 7). niobrarense. 



The incisor present in the premaxilla is of unusually small size in comparison 

 with the cheek-teeth and the size of the skull. P^ has about the same relative 



