Troxell — Diceratherium and the Diceratheres. 201 



Of the six species of rhinoceros named from the John 

 Day beds, D. hesperium (Leidy), D, pacificum (Leidy), 

 D. truquianum (Cope), D. nanum Marsh, D. annectens 

 (Marsh), and D. armatum Marsh, we agree with Peterson 

 that only the last two constitute valid species, although 

 some of the others may give valuable hints on the fauna. 



Fig. 3. 



Fig. 3. — Diceratherium annectens (Marsh). Holotype. Cat. No. 10001, 

 Y. P. M. Premolar teeth with simple parallel lophs. X l/^- 



Fig. 4. 



Fig. 4. — Eestoration of Rhinoceros {Diceratherium) oregonensis Marsh. 

 Holotype. Cat. No. 10002, Y. P. M. Probably the fourth premolar of an 

 undetermined genus from the Mascall formation of the John Day Valley, 

 Ore. X 1/3. 



Rhinoceros {f Diceratherium) oregonensis Marsh, 

 known only by the fragment of a tooth (Cat. No. 10002, 

 Y.P.M., fig. 4), shows the presence of a large, much 

 advanced genus in the Mascall beds of Oregon, compar- 

 able to the Miocene or Pliocene rhinoceroses elsewhere. 



Fig. 5. 



Fig. 5. — Diceratherium armatum Marsh. Holotype. Cat. No. 10003, 

 Y. P. M. Crown view of molars and premolars. Note simplicity of the 

 teeth, molar -like form of premolars, and large size. X 1/3- 



