614 ON SOME NEW FORMS OF AMERICAN BIRDS. 
The six forms diagnosed above appear to be well characterized 
by the distinctive features pointed out; and each one is so char- 
acteristic of the region which it inhabits that at least ninety per 
cent. of the specimens obtained during the breeding season in 
any locality will be typical representatives of one or the other of 
these races. Unless, however, we admit the theory of hybridiza- 
tion, to account for intermediate specimens, and acknowledge it 
especially in this case, it is impossible to consider that any two of 
these forms are distinct specifically, for they are connected by an 
uninterrupted series between the most extreme forms—hyemalis 
and alticola—without a break in the gradual progression from the 
one to the other. Thus, from Sun River, Dakota; Ft. Whipple, 
Arizona; Ft. Bridger, Wyoming, and the McKenzie River district, 
are specimens with the pinkish sides of Oregonus and plumbeous 
back of hyemalis ; or else with black head or rusty back and wings, 
of the former, with ashy sides of the latter; or with the charac- 
ters of the two mixed in various degrees. In the same, manner 
other specimens, from Ft. Bridger, Ft. Whipple, Ft. Burgwyn, 
ew Mexico, Colorado, and the Yellowstone region, have the 
bright rufous interscapulars, ashy head, and black lores of cani- 
ceps with the pinkish sides and rounded outline to the ash of 
breast as in Oregonus; or else they have the rufous spread over 
the wings as in Oregonus, and other characters as distinguishing 
caniceps; other specimens are intermediate between the two in 
various ways. This form was characterized by Professor Baird 
as Junco annectens (Birds Cal., i, 1870, app., p. 564). Among 
the southern Rocky Mountains, and in northern Mexico, speci- 
mens are found which combine perfectly the characters of caniceps 
and cinereus. These have the black and yellow bill and pale ash 
throat of the latter, and the rufous of the back strictly confined 
to the interscapulars as in the former. This form is the J. dor- 
salis of Henry (Proc. Philad. Acad., 1858, 117. Baird, B. N. 
Am., 1858, 467). 
In the effect of climate upon size, altitude appears to have far 
more potency in this group than latitude; thus in tracing these 
forms southward, there is no noticeable decrease in dimensions, 
but on the contrary, the most southern form (alticola) is larger 
than the most northern one (hyemalis). The alpine forms, how- 
_ ever, alticola and Aikeni, are considerably larger than those which 
~ breed at lower elevations. The climatic color-variation in this 
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