BIRDS OF NORTH AND MIDDLE AMERICA. 479 



Chelochelidoa (emendation) Brehm, Isis, 1842, 413. 

 Geochelidon (emendation) Gundlach, Journ. fiir Orn., 1861, 346. 

 Laropis Wagler, Isis, 1832, 1225. (Type, Sterna anglica Montague=-5. nilotica 

 Linnaeus.) 



Medium-sized Sternidae (wing 275-338 mm.) with relatively short 

 and stout bill, short and moderately forked tail, and long tarsus. 



Bill shorter than head, stout, its depth at base equal to nearly 

 half the distance from anterior end of nostril to tip of maxilla, the 

 exposed culmen shorter than combined length of tarsus and first 

 phalanx of middle toe, rather strongly convex or decurved for distal 

 half; gonj^s shorter than outer toe without claw, decidedly shorter 

 than mandibular rami, nearlj^ straight, strongly ascending terminally, 

 its basal angle rather prominent; nostril close to but scarcely touching 

 latero-frontal antia, rather broadly elliptical or narrowly oval, 

 longitudinal; latero-frontal antia only shghtly anterior to malar 

 antia, the mental antia about on line (vertically) with middle of 

 nostril. Wing long and pointed, the longest primary exceeding 

 distal secondaries by twice the distance from tips of the latter to 

 bend of wing. Tail less than half as long as wing, forked for about 

 one-third its length, or less, the lateral rectrices contracted but not 

 attenuated terminal!}'. Tarsus decidedly longer than middle toe 

 with claw; webs with anterior margin moderately excised. 



Plumage and coloration. — Feathers of occiput normal (short and 

 blended). Summer adults with pileum and nape uniform black, 

 the remaining upper parts pale gray, the under parts immaculate 

 white, the inner webs of primaries distinctly bicolored; winter adults 

 with head and neck white, the auricular region and spot in front 

 of eye dusky; downy young mottled or marbled above. (Coloration, 

 in all stages, essentially as in typical species of Sterna.) 



Range. — Europe, south of 55° north latitude, to northern Africa 

 and Australia; Atlantic and Gulf coasts of United States, southward 

 in winter to Patagonia, etc. (Monotypic.) 



GELOCHELIDON NILOTICA (Gmelin). 



GULL-BILLED TERN. 



Adults in breeding season (sexes alike). — Pileum, nape, and upper 

 half of lores uniform deep black; rest of upper parts, including rump, 

 upper tail-coverts, and tail, uniform pale gray (between gull gray 

 and pallid neutral gray) ; entire under parts, including sides of head up 

 to and including auricular and suborbital regions and lower half of 

 lores, together with axillars and under wing-coverts, immaculate 

 pure white; bill wholly deep black; inside of mouth tlesh color (in 

 life); iris dark brown; legs and feet dark reddish brown (dark walnut 

 brown) in life, the soles of toes pinkish brown. 



