1914] Grinnell: Mammals and Birds of the Colorado Valley 159 



way, 1902, p. 210). The entire plumage in obscurus is very much 

 paler than in ater. The former is drab throughout, slightly paler ven- 

 trally and very much paler, more clay color, on the throat; the narrow 

 dusky shaft-streaks on the dorsum, chest and sides are clearly indicated. 

 The female of the eastern form is dark slaty hair brown with less 

 abruptly contrasted grayish throat. 



MEASUREMENTS! IN MILLIMETERS OF THIRTY-ONE MALES OF 



MOLOTHKUS ATER OBSCVBUS FROM THE LOWER 



COLORADO VALLEY 



