PETERSON: THE AMERICAN DICERATHERES. 411 



sedis. It pertains to an animal no larger than, for instance, D. annedens (Marsh), 

 but that is about all I feel justified in positively stating. 



2. Rhinoceros (?Diceratherium) hesperius Leidy,'^ incertce sedis. 



Type. — A third upper molar. Location of the type uncertain. 



Horizon. — Miocene? 



Locality. — John Day region, Oregon. 



The material from the John Day of Oregon, which Leidy finally referred with 

 a question to the Californian species "Rhinoceros hesperius,"^- is, as Leidy himself 

 states, inadequate. The more important features of the remains 

 of the skull appear to be the position and size of the infra-orbital 

 foramen and the position of the base of the zygomatic process of the 

 jugal. Of material referred to R. hesperius Leidy says [I.e., U. S. G. 

 S., Vol. 1, p. 220) : "The anterior extremity of the space included by Fig. 6. Di- 

 the zygoma extends to a line with the interval of the second and he.speri um 

 third molars; in Rhinoceros [Coenopus] occidentalis it extends onlj' to a (Leidy) MK 

 line with the back part of the last molar. The infra-orbital foramen ^ ■'/ 

 is large and occupies a position above the second premolar; in R. [C] 

 occidentalis it is over the third premolar." This description agrees with D. 

 cooki so far as the zygomatic arch is concerned, but the infra-orbital foramen 

 of the latter species is usually opposite the interval between P- and P^ both 

 in D. annedens and D. cooki. In D. annedens the space included by the zygoma 

 referred to by Leidy is slightly more posterior. In comparing the measurements 

 of well-known species of Diceratherium with the figures of specimens referred 

 to R. hesperius and R. pacificus it is seen that M'* of hesperius might well 

 go with the molar of pacificus. So far as the difference in size and even the 

 configurations of the crowns in these teeth go, there is now no valid reason for 

 separating the two on the evidence produced. The tubercle of the median valley 

 of M^ of R. hesperius may well be questioned as a specific character, and is in all 

 probability, as Leidy suggests, "merely an individual peculiarity." In my opinion 

 these remains are generically and specifically unidentifiable, but hold the historic 

 position of being the first material of the Rhinocerotidse obtained in the John 

 Day region of Oregon. 



" Proc. Acad. Nat. Sci. Phila., 1865, p. 176-177; 1870, p. 112; 1871, p. 248. U. S. Geol. Surv. 

 Terr., Vol. I, 1873, p. 220, PI. II, Figs. 8-9. Amer. Jour. Sci., Vol. XXVI, 1908, p. 55, Fig. 5. 



'- Professor Osborn has placed this Californian specimen with Ccenopus platycephalus, "The Extinct 

 Rhinoceroses," Mem. Amer. Mus., Vol. I, 1898, p. 144. 



