Allen.] 214 _ [June 19, 
ern ones, the increased size taking different proportions in different 
species and different styles of bill. Those of a stout, thick, conical 
form generally increase in general size, but especially in thickness. 
Those of a slender, attenuate form become slenderer and relatively 
longer at the southward, with a decidedly greater tendency to curva- 
ture. 
3. Inrespect to the Claws. A similar increase in size is apparent 
.in the claws, especially in that of the hallux, at southern localities, 
perhaps less marked and less general than the increase of es bill, 
with which it evidently correlates. | 
4. In respect to the Tail. A marked elongation of the tail at the | 
southward has been noticed in many cases, both in Cape St. Lucas 
birds (Baird) and in those of Florida. | 
5. In respect to Color. ‘The differences in color are especially ob- | 
vious, and may be reduced to two phases of modification: —(a) a 
general increase in intensity at the southward, and (0) an increase in 
the extent of dusky or black markings at the expense of the inter- 
vening lighter or white ones; or, conversely, the reduction in size of | 
white spots and bars. Under the general increase in intensity the 
iridescence of lustrous species becomes greater, and fuscous, plum- 
beous, rufous, yellow and olivaceous tints are heightened in species . 
with the color continuous in masses. Under the repression of light 
colors the white or yellowish edgings and spots on the wings and tail 
become more or less reduced, and frequently to a great degree, in 
species barred transversely with light and dark colors; the dark bars 
widen at the southward at the expense of the white or lighter ones, 
sometimes to such an extent as to greatly change the general aspect 
_ of the species, as is the case in the Ortyx virginianus of the Atlantic 
States, and in other well known species. Also under the tendency 
to the increase of dark colors, longitudinal streaks and blotches on a 
light ground increase in extent and intensity of color. 
In respect to longitudinal variation, the differences appear to be 
mainly those of color, and to hold a direct relationship to the humid- 
ity of the climate. On the arid plains of the middle and western 
portions of the continent the afnual rainfall is less than half that of 
the eastern half of the continent, while a rainy belt occurs on the Pa- 
cific coast, stretching northward from near the mouth of the Colum- 
bia River to Alaska, over which the annual rainfall is double that of 
any portion of the eastern half of the continent. Taking the species 
that present a nearly continental range, we find that almost invaria- 
