. The American diceratheres. Rhinoceroses, Fossil; Paleontology. 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 tridadylus of the upper Oligocene. The later geological formation in which this new species was found is also to be considered. The. Fig. 12. Diceratherium gregorii. No. 12933, Coll. Amer. Museum. Top of cranium. X i nasa
. The American diceratheres. Rhinoceroses, Fossil; Paleontology. 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 tridadylus of the upper Oligocene. The later geological formation in which this new species was found is also to be considered. The. Fig. 12. Diceratherium gregorii. No. 12933, Coll. Amer. 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. annedens), 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. annedens, 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. annedens, 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 paroccipit
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