428 



University of California Publications. [Geolouy 



from the head of Big Creek, Humboldt County, Nevada, except- 

 ing possibly a more nearly square form ; but it is reasonable to 

 suppose that with more material the fossil form would show some 

 distinct differences between it and the living species. 



Measurements 



Mj, anteroposterior diameter 



M„ transverse diameter 



Callospermophilus 

 No. 12570 trepidus 

 1.9 mm. 1.5 mm. 



1.9 2.3 



10 11 12 14 



Fig. 8. — Citellus, sp. Portion of right mandible with M L . No. 12570, X 4. 



Figs. 9a and 9b. — Mylagaulus monodon. Left P 4 . No. 11572, X 1%. 

 Fig. 9a, lateral view; fig. 9b, superior view. 



Figs. 10, a and b. — Mylagaulus monodon. Left P 4 . No. 11878, natural size. 

 Fig. a, lateral view; fig. b, superior view. 



Figs. 11, a and b. — Mylagaulus pristinus. Eight P 4 . No. 12580, natural size. 

 Fig. a, lateral view; fig. b, superior view. 



Figs. 12, a and b. — Mylagaulus pristinus. Left P 4 . No. 12579, natural size. 



Fig. a, lateral view; fig. b, superior view. 

 Fig. 13. — Eucastor lecontei. P 4 . No. 11085, X 1%. 

 Fig. ll.—Dipoides, sp. Left P 4 . No. 12536, X 1%. 



