PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 1G5 



local influences, gradually less marked toward the habitat of another 

 form, with which it thus intergrades ; and all forms which certaiuly 

 intergrade, no matter how widely distinct the opposite extremes may 

 appear {e. g., Colapies aiiratus and mexicanns), together with intergrading 

 forms whose peculiarities are not exidained by any known " law " of 

 variation, have been reduced to subsjiecific rank. On the other hand, 

 where the diiierence between allied forms is slight, but at the same time 

 absolutely constant, and not coincident wdth a difference of habitat 

 [e. g., certain of the small Thrushes and the various forms of Junco), 

 speciiic rank is upheld. There are someforms w hich future 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 i)resent knowledge, independent of previous 

 conclusions. 

 Smithsonian Institution, January 22, 1880. 



