220 



led me to suspect that it might pertain to the same animal as an isolated 

 molar tooth, from the Mauvaises Terres of White River, Dakota, described 

 under the name of Lophiodon occidentalis. 



RHINOCEROS. 



A number of fossils in the Oregon collection appear to indicate two differ- 

 ent species of Rhinoceros, or perhaps the hornless form Aceratherium. One 

 of them was about the size of the Rhinoceros occidentalis of the Tertiary of 

 the Mauvaises Terres of White River, Dakota, and was first supposed to 

 belong to that species. A more attentive examination of its remains has led 

 to the detection of several peculiarities which render it probable it may be a 

 distinct species. As the specimens co-ordinate in size with the lower jaw 

 from the California Tertiary, on which was founded the R. hesperius, they 

 may perhaps pertain to this species ; and in this view I will so consider them. 

 Of course, more ample material may confirm or refute our position, and may 

 determine the fossils to indicate an animal different from R. occidentalis and 

 R. hesperius. 



The second species, a larger animal, intermediate in size to the latter ones, 

 and the R. crassus of the Niobrara Pliocene Tertiary, has been distinguished 

 with the name of R. pacificus. 



Rhinoceros hesperius? 



The fossils of the Condon collection, attributed with some probability to 

 this species, consist of a mutilated portion of an upper jaw an isolated upper 

 molar, and a lower-jaw fragment containing one entire molar. 



The upper-jaw specimen contains portions of the fangs of the molars, of 

 which there were seven, occupying a space of about 1\ inches, or about 

 equal to that in Rhinoceros occidentalis. 



The anterior extremity of the space included by the zygoma. extends to a 

 line with the interval of the second and third molars ; in R. occidentalis it 

 extends only to a 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. occidentalis it is over the third premolar. 



The upper molar, the last of the series, represented in Fig. 8, Plate II, has 

 nearly the size and form of that of R. occidentalis. As in this, the crown 

 consists of a pair of lobes diverging inward from the antero-external corner. 



