138 Henshaw on the Hermit Thrush. 



have been brought, serve a far more useful purpose in the de- 

 termination of faunal areas than species, which, from their insus- 

 ceptibility to change, i-etain everywhere their peculiar type, the 

 sign manual of specific rank. In the latter case the species cannot 

 be identified with, and its presence relied upon as a factor in the 

 determination of, a restricted avian area, since often its habitat may 

 overlap the boundaries of several such areas ; at all events, its 

 use to this end must take rank far below the variety, which, having 

 been traced to its proper stock, and the exact amount and manner 

 of variation noted, serves a very important end as denoting by the 

 changes it successively exhibits the limits of climatic and other in- 

 fluences corresponding to definable geographical limits. 



An excellent illustration of this occurs to us in the cases of the 

 Song and Lincoln's Sparrows (J/, meloda and allies and lincolni). 

 The first, from its pliability of organization, so to speak, passes 

 through several successive phases of color change, as we cross its 

 habitat from east to west, as well as variations of bill, etc. These 

 in each instance serve for the discrimination of a race which is 

 identifiable more or less closely with a limited province. The latter, 

 on the contrary, with a general range almost coextensive with the 

 former, reaching from the Atlantic to the Pacific, and over no small 

 portion of which it is foimd breeding, appears nowhere to vary ap- 

 preciably; hence, while interesting from this very fact, it is of very 

 limited value in the consideration of questions touching faunal 

 boundaries. 



A few words may be said upon color as a means of identification 

 of the forms here under consideration. The two Western, audu- 

 honi and namts, ai-e essentially alike in this respect, at least so far 

 as dried skins are concerned ; as, however, they stand at the oppo- 

 site extremes of size, confusion between them is scarcely to be 

 looked for. The Eastern bird, ^ja//a.«?', differs from either in color, 

 and very appreciably. The dorsum has a distinct reddish-brown 

 tint, while the flanks are decidedly fulvous ; in the others these 

 colors are rephiced by a rather pure gray. The smaller specimens of 

 jmllasifrom Eastern localities may be instantly selected from a series 

 of the Western namis by these points of color, without appeal to the 

 localities on their labels. 



In conclusion, it is worthy of note that while the mountain-in- 

 habiting T. auduhoni shows a marked superiority in size to pallasi in 

 general bulkiness of body and in wings, bill, and tail, its tarsus not 



