202 Troxell — Diceratherium and the Dicer atheres. 

 Dicer atherium lohatum, sp. nov. 



(Fig. 6.) 



Holotype, Cat. No. 12487, Y. P. M. Probably from the true Diceratherium 

 zone, Turtle Cove, John Day River, Oregon. 



The liolotype consists of the anterior portion of a 

 skull, collected in 1875 by William Day. Although 

 slightly smaller than D. armatum, the new species shows 

 a much greater complication of enamel, in which respect 

 it is more advanced in its evolution ; but it is more conser- 

 vative in that it still possesses two incisors (see fig. 1 

 Ay B, and C, comparing referred specimens of D. arma- 

 tum). 



Dentition. — The premaxillaries are quite slender, both 

 laterally and vertically, and extend well beyond the 

 premolars. The first or median incisors are smaller in 

 antero-posterior dimension than even those of D. annec- 

 tens (see fig. 1) and are rounded and lobate rather than 

 elongated and pointed in front. P is more than half as 

 large as P, an unusual thing for this tooth is commonly 

 very small or absent. Both teeth are rounded and lobate 

 as viewed from the side and resemble the form of an elk 

 tooth ; it is this feature which suggests the specific name. 



Fig. 6. 



/y^ r^j^r ^ 



Fig. 6. — Diceratherium lo'hatum, sp. nov. Holotype. Cat. No. 12487, 

 Y. P. M. Crown view of premolars and molars, excepting M^, showing the 

 complication of enamel and the cross ridges united by the ^'mure^', m, a, 

 wall across the median valley. The designations of the ridges or lophs: 

 ectoloph, protoloph and metaloph, apply both to molars and premolars; D, 

 deuterocone, and T, tetartocone, to the premolars; Pr, protoeone, and Hy, 

 hypocone, to the molars. See also figure 1 C for premaxillary and incisors of 

 the same specimen. X 1/3. 



The premolars are distinctly bridged from loph to 

 loph and united by a wall, which may be technically known 

 as the mure, projected across the median valley effect- 

 ively damming it up in such a way as to form the deep 

 central pit completely surrounded by an enamel border. 



