8 



University of California Publications in Geology 



[Vol. 9 



column. Hipparion mohavense of the Ricardo Pliocene seems to be 

 the nearest form among the species west of the Wasatch. The Ellens- 

 burg species seems to differ from H. mohavense in flatness of the outer 

 walls of the protoconid and hypoconid and in the greater prominence 

 of the anteroexternal angle of the protoconid. Both of these char- 

 acters may be due to combination of age and individual characters. 

 The habit of the teeth in the Ellensburg specimen suggests that addi- 

 tional material will show more rather than fewer differences separ- 

 ating this form from the H. mohavense. Neohipparion leptode of the 

 Thousand Creek Pliocene and an allied form from the Rattlesnake 

 Pliocene differ from the Ellensburg specimen in the presence of a very 

 strong anteroexternal ridge on the hypoconid. 



Although Hipparion has been listed as occurring in the Mascall, 

 Middle Miocene, the writer knows of no occurrence that can certainly 

 be stated to be located within the limits of that formation. Unless 

 it be true that Hipparion actually occurs in the Mascall, it seems that 

 the Ellensburg formation may be of considerably later date than the 

 beds containing the typical Mascall fauna of the John Day Valley in 

 eastern Oregon. 



Measurements 



Hipparion Hippai'ion 

 condoni, Merychippus, mohavense, 

 Ellensburg Barstow Ricardo 

 No. 668 U. O. No. 21459 No. 19785 



P 4 , anteroposterior diameter 21 mm. 24.7 23.8 



P 4 , transverse diameter across protoconid 11.1 12 11.9 



P 4 , anteroposterior diameter of metaconid-meta- 



stylid column 12.6 9.1 14.7 



P 4 , height of worn crown 31 44 32 



M„ anteroposterior diameter 17.6 25.4 



M,, transverse diameter across protoconid 10.3 10.1 



Mj, anteroposterior diameter of metaconid-meta- 



stylid column 11.2 9.9 



Hipparion, Merychippus, 



Ellensburg, Barstow 



No. 672 U. 0. No. 21776 



I„ anteroposterior diameter 8.3 l.i 



I„ transverse diameter S.3 



L, anteroposterior diameter 8.3 /./ 



I 2 , transverse diameter 12.1 6.5 



I„ anteroposterior diameter 7.4 



I S) transverse diameter 12 



Transmitted June 7, 1915. 



5.7 

 5.9 



