414 MEMOIRS OF THE CARNEGIE MUSEUM. 



comparable in size with this species. On the whole the configuration of the crowns 

 of these teeth, as represented, does not greatly disagree with that of the type of 

 D. niobrarense; one of the teeth being of a considerably younger individual than 

 the latter. The size of the species of Loomis is, however, decidedly larger than 

 D. niobrarense. If this does not prove to be a very large individual of the latter 

 form, it may be a distinct species; possibly in a more direct line from the large 

 form D. cjregorii sp. nov., of the lower Rosebud beds of South Dakota (See page 421). 



6. Diceratherium armatum Marsh."' (Plate LVII and text-figure 10.) 



Type. — Complete skull somewhat crushed dorso-ventrally. Bones of fore 

 foot associated. Peabody Museum of Natural History No. 10,003. 



Horizon. — Lower John Day Formation (?Lowermost Miocene). 



Locality. — Near John Day River in eastern Oregon. 



As is well known, the genus Diceratherium established by Professor 0. C. 

 Marsh in 1875 rests on this famous specimen in the Peabody Museum of Natural 

 History. The type was only briefly described by Marsh. Since that time no 



Fig. 10. Diceratherium armalum Marsh., No. 10003, Coll. Peabody Museum of Natural History. 



Top of cranium. X 1. 



complete illustrations or detailed description of its osteological structure have ap- 

 peared. For the purpose of more detailed records the writer was accorded the 

 privilege of studying the type material in the Peabody Museum. The descriptions 

 and illustrations of the type material follow the modified generic determination 

 of Diceratherium and the specific characters of D. armatum. 



Generic Characters Established by Professor Marsh (Modified). 



Males with osseous protuberances on the anterior portion of the nasals. Females 

 ranging from those with light or incipient nasal protuberances to those with nasals 

 more or less smooth. Incisors -§•, Canines 1,--^ [in rare cases a very minute canine per- 

 sists]. Premolars f, Molars f. Fore and hind feet functionally tridactyl. 



'« Amer. Jour. Sci., Vol. IX, 1876, p. 242; Ibid., Vol. XXVI, 1908, p. .54, Fig. 2. 



