10 NOMENCLATURE OF NORTH AMERICAN BIRDS. 



press of climatic or 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 (e. g., Golaptes auratus, and C. mexicanus, and the 

 different races of Passerella), together with intergrading forms whose 

 peculiarities are not explained by any known "law" of variation, have 

 been reduced to subspeciflc rank. On the other hand, where the differ- 

 ence between allied forms is slight, but at the same time apparently 

 constant, and not necessarily coincident with a difference of habitat (e. g., 

 certain of the small Thrushes and the various forms of Junco), specific 

 rank is upheld. There are some forms which 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 consistent 

 as possible, giving the rank of each form as it appears in the light of 

 our present knowledge, independent of previous conclusions. 



