S. SUPEECILIARIS VAE. ANTILLARUM, LEAST TERN. 693 



DiAG. S. minuUv simiUs cjusdemque staturcc ; sed nropygio conddfjne cum palVw concolori- 

 ' bus, rostro Ireviore, graciUure, rlitd frontuli uiujustiore ; roatro Jiavo, ajjice )tigro, 2)cdibus 



flavis. 



Hah. — Temperate North America, especially along the Atlantic coast of the United 

 States, but also on the larger inland waters. Up the Pacific coast to California (Xantus, 

 Coues). South into the Antilles and Middle America generally. Apparently winters 

 beyond the United States. (The typical su2)erciUaris iroui South America; Brazil, Para- 

 guay, &c.) 



Lieutenant Warren's Expedition.— 900o,F\atte River; 9007, Loup Fork ; 8999, Yellow- 

 stone River. 



Adult, breeding j^li'tnage. — Bill about as long as the head, slightly exceeding the tarsus 

 and micldle toe together without the claw ; compressed; only moderately robust; tho 

 tip very acute, but not much attenuated nor decurved. Culmen straight to the nos- 

 trils, slightly but equally decurved for the rest of its extent ; commissure curved 

 throughout; rami concave in outline, shoit; gonys straight, much longer than the 

 ramus. Nasal groove tolerably wide, but very short, ;iud not deep. Tomia slightly 

 inflected. Wings of moderate length ; first primary but very slightly longer than the 

 second ; the rest successively more and more rapidly graduated. Tertials and inner 

 secondaries very short, reaching in the folded wing only half way to its tip. Tail 

 rather short, and only moderately forked ; the central rectrices broad, with broadly 

 rounded tips ; the external pair narrowing rapidly to a very acute tip. Tibiaj bare but 

 a very short distance. Feet small, short, slender; tarsus equal to middle toe and half 

 its claw ; of ordinary characters as regards scutellatiou and reticulation. Outer toe 

 almost or quite as long as the middle, with its claw very much shorter and weaker; 

 inner toe short, its claw just reaching to the base of the middle claw. Unguis of hal- 

 lux extremely minute. Webs moderately broad; the outer only slightly, the inner 

 very considerably, incised. 



Bill yellow, its tip for usually an eighth to a fourth of an inch black, but sometimes 

 altogether yellow. The junction of this black with the yellow is quite straight and 

 perpendicular, as it does not run oft' on the gonys, uor culmen, nor tomia. Pileum 

 glossy greenish-black. On the forehead a narrow lunula of white, the posterior border 

 of which is very concave, the narrow cornua of which extend over the eyes just to 

 their i)osterior borders. This crescent extends quite to the bill, but is separated from 

 the white of the cheeks by a narrow line of black, which runs forward as a prolonga- 

 tion of the pileum, through the eyes, to the extreme tip of the feathers on the side of 

 the bill. The entire upper parts of the bird, including its rump, nape, upper tail- 

 coverts, and the rectrices themselves, are pearl-blue, with a considerable tinge of 

 ])lunibe()us. This color extends uudiluted quite to the black pileum, on the sides of 

 the neck and head fading insensibly into the pure white of the under imrts. The rec- 

 trices are about the color of the back, only they grow lighter toward their bases, and 

 their under surfaces, together with the outer web of the first, are nearly white. The 

 color of the hack extends undiluted to the extreme apices of the secondaries and ter- 

 tials, but the inner webs of these feathers are basally nearly white. Tho shafts of the 

 first two primaries are white interiorly, black superiorly; the webs themselves black, 

 the inner with a coTisiderable space white; this white space separated from the black 

 by a tolerably distinct Hue of definition, not extending to the tip of the feather. The 

 other primaries are a considerably darker shade of tbe color of tho back, their inner 

 wel)s fading into whitish along their borders, which thus become conspicuously mar- 

 gined with white quite to their tips. Whole under parts, including tho inferior alar 

 tectrices, i)ure white, without the least wash of i)lumbeous or tinge of rosy. Feet 

 orange yellow, the claws black. 



Toward the middle or latter part of July, the bird above described begins to change, 

 and, until it has fully coiupleted its autumn moult, its jdumage is as follows: 



Adults during the Angu-sl moult. — Bill mostly black, but a greater or less degree of 

 yellow renuiining. The black pilcuiu has already become variegated with white, the 

 front being mostly of that color. The u))per parts are as in summer, but there are 

 indications of the <lusky band that is to appear ahmg the fore-arm. Tail scarcely at 

 all forked, from wearing away of the central rectrices. A larger number of the pri- 

 maries are blackish, without a silvery tinge, and this grayish-bhick extends along the 

 radial edge of the metacarpus to tlu- carpal joint on the feathers of the ala spuria. 



At tlie finishing of the moult, we have the — 



Adult, uinter plumage. — Bill black ; legs and feet dull yellowish. Forehead and lores 

 pure white; \t'rtex white, with more or less numerous, narrow, longitudinal Hues of 

 black; occiput and nape wholly brownish-black, sending forward on each side over 

 the auriculars, to just in front of the eye, a band of the same. The ui)per i)arts are as 

 in the adults in summer, but rather darker, and the mantle does not, as iu summer, 

 extend (luitc; up to the nape, liut leaves .a portion of the neck beliiud white, as are also 

 the whole under paits. There is a continuous band of gra.\ isli-black along the fore- 

 arm ; the bend of the wing from the primaries to the carpal joint is also of this color. 



