198 Troxell — Dicer atherkim and ihe Diceratheres. 



Dicer athermm nanum (Marsh) 1875. Holotype, Cat. 



No. 10004, Y.P.M. 

 Dicer atlierium truquianum (Cope) 1879. Holotype, 



A.M.N.H. (Cope Coll.), Cat. No. 7333. 

 ^ fDiceratherium oregonense (Marsh) 1873. Incertse 



sedis. Holotype, Cat. No. 10002, Y.P.M. 

 Dicer atlierium lohatum, sp. iiov. Holot^^e, Cat. No. 



12487, Y.P.M. Fig. 6. 

 Dicer atlierium cuspidatum, sp. nov. Holotype, Cat. No. 



12007, Y.P.M. Fig. 7. 



The True Diceratheres. 

 Dicer atlierium Marsh. 



The genoholotype, D. armatum, based on a large skull 

 (Cat. No. 10003, Y.P.M., ^g. 5) from the middle John 

 Day beds of Oregon, has unusually simple teeth and 

 enlarged broad nasals with rugosities not rounded, but 

 elongated antero-posteriorly, separated and directed 

 outward. Its size and the simple, primitive teeth make 

 us think that the living conditions were not severe, that 

 there was an abundance of nourishing food, and a moist 

 climate. The molars resemble those of Metamynodon. 



Diceratherine species from the Great Plains are here 

 separated from Dicer atlierium Marsh and put under 

 . separate generic groups: Metaccenopus Cook and Meno- 

 Y ceras, gen. nov. ^ 



The species with simpler teeth, of larger size but with 

 more subdued nasal eminences, belong with the genus 

 Metaccenopus, genoholotype M. egregius Cook. The 

 ' smaller animals from the Agate Spring quarry, of 

 slightly later age, with teeth more progressive in their 

 subhypsodonty and in the development of additional folds 

 of enamel, with horn rugosities even more prominent 

 than in Dicer atlierium, are grouped under Menoceras 

 nobis, the genoholotype of which, D. coohi Peterson, is 

 defined later. 



Dicer atlierium armatum Marsh. — The following points 

 may serve in part to define this species: (1) males with 

 well developed, widely separated, oval rugosities on 

 the nasals in maturity; (2) moderate deepening of 

 sinuses and pits of teeth, or increase in height of ridges, 

 reaching an extreme in later rhinoceroses {fD. Oregon- 



