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, retain 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 mf. melodct and allies and Jincolni). 
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 found 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- 
boni and nanus , are 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, 'pqdlasi , 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 replaced by a rather pure gray. The smaller specimens of 
joallasi from Eastern localities may be instantly selected from a series 
of the Western nanus 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. auduboni shows a marked superiority in size to pallasi in 
general bulkiness of body and in wings, bill, and tail, its tarsus not 
