1914] Grinnell: Mammals and Birds of th( Colorado Valley 223 



The range of harrisi is practically restricted to Arizona and parts 

 of Sonora. The range of leucurus and its geographic races almost 

 completely surrounds that of harrisi. But, as far as I know, the 

 ranges of the two nowhere overlap, nor has there been found any 

 case of hybridization between the two. It is certain that only the 

 existence of the Colorado River keeps the ranges of the two separate 

 in this segment of their respective peripheries. What would have 

 happened if the river had not served as an absolute barrier is. of 

 course, wholly conjectural. But there is no doubt in my mind that in 

 such event both the ranges and the characters of the two forms 

 would be far different from what they now are. 



LIST AND MEASUREMENTS IN MILLIMETERS OF AMMOSPEBMOPBILUS 

 LEUCUSUS LEUCURUS, FROM THE CALIFORNIA SIDE OF 

 THE COLORADO RIVER 



Not averaged; tail defective. 



