80 University of California Publications in Zoology [Vol. 21 



upon a paper to facilitate the outlining of a map. The fact that I 

 place certain groups of birds witliin certain adjacent squares must 

 not be construed as a belief that the two are essentially different 

 from one another in just the same way as all other "subspecies" are, 

 and that such differences persist to the edges of each square. Radical 

 differences do exist between certain closely adjacent subspecies of 

 Passerella; they undoubtedly do not exist between certain others here 

 recognized. It is simply most convenient to utilize subspecific names 

 as is here done, provided it be understood just what they stand for. 

 I wish to make it clear that in my own mind the whole treatment 

 here accorded the different forms of Passerella iliaca is but an outline, 

 correct as far as it goes, I trust, but with much detail still to be filled 

 in. I have had the advantage of far greater series of specimens, from 

 many more localities, than any previous student of the group. This 

 material has been carefully and leisurel}^ studied, I have arranged the 

 observed facts and drawn my conclusions to the best of my ability, 

 and I have checked up my results in various ways. I believe my con- 

 clusions are sound as far as they go, but it will be seen that necessarily 

 many deductions have been drawn from, and hypotheses erected upon, 

 data derived from winter birds. A satisfactory^ demonstration of the 

 truth of such conclusions is to be attained only after the accumulation 

 of more material and of much additional information as regards 

 conditions in the summer homes of the several forms, notably so as 

 regards variation at the margins of these habitats. It is not only 

 specimens that are required, but careful study of the living birds in 

 their natural surroundings. 



Material and Methods of Treatment 



There are 717 specimens of Passerella catalogued to date in the 

 collection of the Museum of Vertebrate Zoology. An especially 

 valuable feature of this collection of fox sparrows lies in the extensive 

 series of breeding birds from points on the northwest coast and from 

 the mountains of California. Private collectors in California have, 

 in the mass, accumulated large numbers of these birds, mostly winter 

 visitants, and in a great many cases such collectors have sent their 

 specimens to this Museum to be identified. The loan was solicited 

 of all private series known to be existent in California, and in every 

 case this privilege was freely granted and the specimens suffered to 

 remain here as long as they were needed. A preliminary survey of 



