BIEDS OF XORTH AND MIDDLE AMERICA. 659 



"iiood" (only in summer plumage, however), and a similar (solored 

 bill, but resembles it in no otlier respect. Creagrus diffei's, indeed, 

 from XeTTia 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 

 bill is very peculiar in shape, being mucli 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-eiglith of its 

 length. As to coloration, there is even greater difference, Creagrus 

 having the dark "hood" descending much farther down ovei the neck, 

 and instead of being ver}^ abruptlj^ terminated by a black border has 

 no very definite outline except on the f oreneck ; while the white patch 

 at the base of the upper mandible and the veiy conspicuous white 

 stripe margining the exterior scapidars 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 Creagriis is a large gull, about the size of Larus dela- 

 imrensis, while that of Xema is hardly so large as Chroicocej^Jialus 

 pMladelpMa; and with its dark colored liead, deep red feet, and deeply 

 forked tail ought to be very easily identified at a considerable distance. 



CREAGRUS FURCATUS (Neboux). 



SWALLOW-TAILED GULL. 



Adults (sexes alike).* — -Head and upper neck, all round, uniform 

 dull slate color (or between deep neutral gray and dark quaker 

 drab), relieved by a white spot mvolvmg 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 defhied on foreneck, but laterally and posteriorly fading 

 graduaUy mto light neutral gray on lower neck, the chest and side 

 of breast pale neutral gray, fading gradually into white on remaining 

 mider parts ;'= back, rump, scapulars, tertials and proximal wing- 

 coverts uniform neutral gray, the outermost scapulars broadly and 



a Clifford, Proc. Calif. Acad. Sci.. 4th ser., ii, 1913. ,37. 



<> 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 Laridse. 



c The white of under parts is often tinged with eosine pink in recently killed 

 specimens. 



