BIRDS OF NORTH AND MIDDLE AMERICA. 659 
“hood”? (only in summer plumage, however), and a similar colored 
bill, but resembles it in no other respect. Creagrus differs, indeed, 
from ema in so many decided characters, affecting form even more 
than coloration, that I am compelled to regard it as one of the most 
strongly characterized genera in the family. 
From Xema, the points of difference are many and decided. The 
pill is very peculiar in shape, being much deeper at the base than else- 
where and strongly decurved at the tip; that of Xema being much 
smaller proportionally, much straighter, and much deeper through the 
angle than at the base. The tail is relatively much longer and much 
more deeply forked, being nearly half as long as the wing and forked 
for about one-third of its length, while that of Xema is much less than 
half as long as the wing and forked for not more than one-eighth of its 
length. As to coloration, there is even greater difference, Creagrus 
having the dark ‘‘hood’’ descending much farther down over the neck, 
and instead of being very abruptly terminated by a black border has 
no very definite outline except on the foreneck; while the white patch 
at the base of the upper mandible and the very conspicuous white 
stripe margining the exterior scapulars are entirely peculiar features. 
Moreover, the dark ‘‘hood”’ is apparently a permanent feature, there 
being no distinctive winter or non-breeding plumage,’ and the colora- 
tion of the young is quite distinct in character. 
The type of Creagrus is a large gull, about the size of Larus dela- 
warensis, while that of Xema is hardly so large as Chroicocephalus 
philadelphia; and with its dark colored head, deep red feet, and deeply 
forked tail ought to be very easily identified at a considerable distance. 
CREAGRUS FURCATUS (Néboux). 
SWALLOW-TAILED GULL. 
Adults (sexes alike).2—Head and upper neck, all round, uniform 
dull slate color (or between deep neutral gray and dark quaker 
drab), relieved by a white spot involving antero-lateral portion of 
forehead and a very small white spot at point of malar antia (the 
latter sometimes obsolete), the dark gray or slate color more or less 
abruptly defined on foreneck, but laterally and posteriorly fading 
gradually into light neutral gray on lower neck, the chest and side 
of breast pale neutral gray, fading gradually into white on remaining 
ynder parts;* back, rump, scapulars, tertials and proximal wing- 
coverts uniform neutral gray, the outermost scapulars broadly and 
@ Gifford, Proc. Calif. Acad. Sci., 4th ser., ii, 1918, 37. 
6 According to Gifford (Proc. Calif. Acad. Sci., 4th ser., ii, 1913, 37) there seems 
to be no seasonal change in coloration in this species, in which respect it differs from 
most if not all other Laride. 
¢ The white of under parts is often tinged with eosine pink in recently killed 
specimens. 
