260 



University of California Publications. 



[Geology 



walls surrounding the impressed areas on the outer side of the 

 paracone and metacone is so different from the much more 

 gently curving lines of the outer side of tooth no. 11570 as to 

 suggest that the two teeth represent different species ; they may, 

 however, belong to the same form. 



From such evidence as is available it seems probable that none 

 of the specimens of Hypohippus from the Virgin Valley region 

 are identical with II. equinus though, as suggested by Gidley, 

 the difference is very slight. The upper molar represented in 

 no. 12564 is apparently near to H. osborni, but not actually 

 identical with it. The lower molars of series no. 11760 differ 

 quite distinctly from H. equinus in width and in the smaller size 

 of P 1 . According to the measurements which Dr. W. D. Matthew 

 has kindly furnished, the lower molars of H. osborni show rela- 

 tively greater width than in H. equinus, as in the upper molars. 

 The lower molars of the Virgin Valley forms are somewhat larger 

 but especally wider than those of II. equinus. They are some- 

 what smaller than the corresponding teeth of the type specimen 

 of H. osborni, but approach this form a little more closely than 

 to //. equinus. 



Measurements 



H. II. 



osborni* equinus 

 25.7 mm. 25 



II. 



ajfi His 



No. 

 12587 



28.7 



27 







27. 



25 







29.9 



26 







27.2 



25 







31. 



28 







23.3 



25 







31.5 



27 







21. 



21 







27.8 



22 







76.5 



78 





72. 



8.5 



13 





7.4 



6.2 



6 







24.2 



21 





22.8 



14.5 



9 





14.5 



23.9 



22 



28. 



22.7 



17.4 



13 



20. 



17.7 



No. No. 

 11570 12564 



23.1 



28.6 



21. 

 27.2 



P 1( anteroposterior diameter 



P,, transverse diameter 



P 2 , anteroposterior diameter . 

 P„, transverse diameter 



" The dimensions of the inferior dentition were kindly furnished by Dr. W. D. 

 Matthew. 



