PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 165 
local influences, gradually less marked toward the habitat of another 
form, with which it thus intergrades; and all forms which certainly 
intergrade, no matter how widely distinct the opposite extremes may 
appear (¢. g., Colaptes auratus and mexicanus), together with intergrading 
forms whose peculiarities are not explained by any known “law” of 
variation, have been reduced to subspecific rank. On the other hand, 
where the difference between allied forms is slight, but at the same time 
absolutely constant, and not coincident with a difference of habitat 
(e.g., certain of the small Thrushes and the various forms of Junco), 
specific rank isupheld. There are someforms whichduture investigation, 
based upon adequate material, may decide to be of different rank from 
that accorded them here. We cheerfully acknowledge our fallibility, 
but at the same time would say that we have endeavored to be as con- 
scientious and consistent as possible, giving the rank of each form as it 
appears in the light of our present knowledge, independent of previous 
conclusions. 
SMITHSONIAN INSTITUTION, January 22, 1880. 
