XEMA FUECATUM, SWALLOW-TAILED GULL. 661 



DiAG. X. minor, caudd evmrginatd, capite cucullato, collo torquaio, rosiro nigra apice flavo, 

 pedibus nigris^ Long. tot. 14.00 ^oH. 



Hai. — Arctic regions of toth liemispheres. Spitzbergen. In America, south in win- 

 ter to New York, and Great Salt Lalce, Utah. 



Adult, breeding plumage. — Bill black to the angle, abruptly bright chrome from angle 

 to tip. Mouth bright orange ; eyelids orange ; legs and feet black. Hood uniform clear 

 deep slate, bounded inferiorly by a ring, narrowest on the nape, of deep velvety black. 

 Lower part of neck all round, tail and its coverts, four inner primaries, secondaries, 

 greater part of greater coverts, tips of tertials, except the innermost, and whole under 

 parts, pure white. Mantle slate-blue, extending quite to the tips of the inner tertials. 

 Edge of wing, from the carpal joint with the bastard wing, black. First live prima- 

 ries, with their shafts, black ; their extreme tips, and the outer half of the inner webs, 

 to near the end, white. Other primaries white, the sixth with a touch of black on the 

 out/sr web. Emargination of tail 1.25 inches. 



Dimensions. — Length, 13.75 ; wing, 10.75; bill, 1 ; along gape, 1.50 ; height at angle, 

 0.30 ; tarsus, 1.25 ; middle toe and claw, same. 



Yming-of-the-year.—i'So. 50182, Plover Bay, Sept. 1867.) Tail forked, nearly as in the 

 adult. Bill small and weak, flesh-color and dusky. Legs apparently flesh-colored. 

 No hood nor collar. Most of the head, the back of the neck, and upper parts in gen- 

 eral, slaty-gray, transversely waved With brownish-white ; each feather being tijipied 

 with this color. Under parts white. Tail white, wiih a broad teiminal bar ot black, 

 an inch wide on the central rectrices, growing narrower on the others successively ; on 

 the outermost sometimes iuvading only one web. This black bar very narrowly edged 

 with white. Wings surprisingly similar to those of the adult, but the white on ihe 

 inner webs more restricted, and the white tips very small or wanting altogether. 

 Dimensions a little less than those of the adult. 



The pictura of the primaries in the above-described specimen is remarkably like the 

 adult's, considering how young the specimen is; but I presume the condition is con- 

 stant, or at least usual. As the bird advances toward mai uritj the primaries gain more 

 decided white tips ; the black bar disappiars from the tail ; the upper parts become 

 first mottled with the clear pearl-blue of the adnlts, then lose altogether the feathers 

 of the present hue and pattern. Exactly at what time the hood and collar are assumed 

 I cannot say ; I should j adge not till the second year. 



The yellow tip of the bill varies greatly in size. Half of the bill may he yellow ; 

 or the yellow may be reduced to nil ; but birds with an entirely black bill are not often 

 seen. The adult winter plumage I have not seen, and cannot say Whether the hood is 

 lost or not; but I should judge, from analogy, that it is not retained. The species 

 varies less than most Gulls ; in fact I have little to add to the above on this score. The 

 bill varies, as usual, in length and stoutness. Young birds look something like young 

 Chrcecocephalus Philadelphia, bnt I believe the tail is always at least emarginate. 



This species was first in i reduced in 1818 by Capt. J. Sabine as I.arus sabinei, but its 

 peculiarities were almost immediately made the basis for generic separation by Leach. 

 Macgillivray referred it to the genus Gavia. I have not been able to verify Bouiiparte's 

 quotation of " Lai~us collaris Sabine." The same author incorrectly gives Leach as 

 authority for the specific name. 



XEMA FUECATUM, (Neb.) Bruch. 



Swallow-tailed Gull. 



Motiette a queue fourchiie, Neboux, Eev. Zool. iii, 1840, 290. 



Larus furcatus, PuBV. & Des Muhs, Zool. Voy. Venus, Ois. 1855, 277, pi, 10. 



Xenia furcatum, Bkuch, J. f. O. 1853, 103.— Codes, Key, 1872, 317 ; Check-list, No. 559, 



Creagrus furcatus, Bp., " 1854."— Bbuch, J, f. O. 1855, 292.— Bp., Compt. Eend. 18.jC, 



771.— Lawe., B. N. a. ]fc58, 8.J7.— CouES, Pr. Phila. Acad. 18b2, 312.— Blas., 



J. f. O. 18t)5, 370. 



DiAG. " L. supra cineracrus, eapitecolloquef uliginos^ nigrcscmlibus ; eubUis albus ; atrigdpost- 

 oculari et basi frontali albis ; palpebrit- aurantiis, tarsis palmisque rubris." 



Sab. — Coast of California, f?) Also, Arctic regions. 



Adult. — Bill of moderate robustness, much bent at the tip, black at its base, white 

 toward its apex, with "a small rounded white spot on either side oi the base of the 

 upper mandible." Tarsi, toes, and interdigital membranes, red ; the claws black. 

 Irides red. the [edges of the] eyelids orange. Head, and greater part of the neck all 

 round, black [_" gris brun," Neboux; "/uliginose nigresceniibus," PnE^'OS•r and Des 

 MUES]. Mantle light gray I" blanc gris," Neboux]. Breast, belly, under surfaces of 



the wings, and the tail, pure white. The folded wings reach inches beyond the 



tail. Primaries bordered both internally and ex.ernally with black. Middle wing- 



