LARUS EBURNEUS, IVORY GTJLL. 649 



DiAG. L. corpore toto albo, rhaehidibus remigum flavis, pedibus nlgris, rosiro rirescotte-flavo. 

 Hob. — Arctic seas, coming southward in winter. 



Adult, breedhn/ phmuuje. — Culraen straight to tlie nostrils, then regnhirly convex ; 

 commissure gently curved to the tip, where it is considerably decuived ; gonys straight 

 to near the anglf, which is well defined, the outline from angle to tip perfectly straigLit. 

 Feathers extending between the rami nearly to the angle. Wiugs long and pointed, 

 reaclHng beyond the tail ; primaries gradually attenuated to the tip. 



Entirely pure white, the shafts of the primaries straw-yellow. Bill dusky greenish, 

 yellow at tip and along the cutting edges. Legs and feet black. 



Yotnifi. — Front, chin, and sides of the head, grayish dusky ; the upper part nf the neck, 

 all round, irregularly spotted with the same. Scapulars, and upper and under whig- 

 coverts, spotted with brownish-black, the spots most numerous along the lessor coverts. 

 Tips of the primaries and tail feathers with a dusky spot. Otherwise as in the 

 preceding. 



Dimensions. — Length, 19.50 ; wing, 13.25; bill above, 1.40: along gape, 2.10; height at 

 nostrils, 0.45; tai'sus, about 1.45: middle toe and claw, 1.75. 



The bill of this species, in iive specimens before me, varies greatly in size. The dif- 

 ference in .shape is also quite notable. But it is in the tarsus that the greatest variations 

 are found. The shortest tarsus before me measures but 1.20. This would nearly do for 

 the Larus brachytarsus of Holboll, but the other characters do unt correspond with tho.se 

 given by that author. This specimen is from Mr. Audubon's collection, and corresponds 

 minutely with his plate. 



The present being a bird of such marked character, there are no questions of doubt- 

 ful synonymy which here need special mention. The quotations " alhiis Scha'fr'er, 1799," 

 and candidna Fabricius, as well as niveiis Martens, are all undoubtedly referable to the 

 present species. The other synonyms of the species arise chieriy from the various gen- 

 era to which the bird has been referred. There is no reasonable doubt that the supposed 

 " L. brachytarsiis" is the same bird ; the description gives no tangible characters. 



Suhgenus Chrceoocbphalus, Eyton. 



= Xema, Boie, Isis, 1822, 563, uec Leach. 



> Gavia, Kaup, Sk. Eut. Eur. Thierw. 1829, 99 (Z. ridibundus), nee Mohk. 



> Ichilnjaiitus, Kaup, op. cit. 99 (X. ichllijiwlns, Pall.). 

 ^ HiidrocnlocKS, Kaup, op. cit. 99 {L. miuntns, Pall.). 



— CinviamphaUis. Eyt., Cat. Br. B. 1830, 53 {L. capistratus, Temm.).— Lawk., B. N. A. 



1858, 850.— CouES, Pr. Phila. Acad. 1862, 309. 

 X Oana, Macgil., Man. Orn. ii, 1842, 239, nee Moiiii. 

 ~y Atrivilla, Bp., 1854 {A. cattsbwi, Bp.). 



> McUigaria, Bp., 1854 {L. franklini). 



> Cirrhoapltahis, Biu'cii, J. f. O. 1855, 288 (i. cirrhoccphalus, Vieill.). 

 =; Chracoccphahts, STniCKL.— CoUES. 



= Cliroocephahis, Scl. & Salv, 



Chak. Form as in Lams proper, but general organization less robust (with some 

 exceptions) and the lull usually weaker, slenderer and more acute, and less hooked. 

 Head enveloped in a hood in the breeding season, and white of under parts then usually 

 ro.sy-tinted. Tail s(pu\re, or nearly so. 



There are no marked peculiarities in form of this group, the pattern of colorntion 

 being maiuly its basis. The species average smaller thau those, of Larus proper, though 

 the C. i(lilli!/((i'lus is among the largest of the subfamily. The group ajiprdximates to 

 A'<'H((/ and L'li<)(,lostilliit( in nearly all respects, but the tail is neither foiketi nor cuueate. 

 Its sub(li\ ision, as indicated in tlm above synonymy, is entirely unre(iuiretl. 



There- are but three established North Aiuc^rican species; the ('. curullalus juKving to 

 be the same as (.'. fraukliui, while ('. miuulus is not proven to inhabit this couutiy. 

 These species may be tabulat<!d as follows: 



Analysis of sjHcicn. 



(I. Tarsus longer than the nnddle ttx" and claw. 



I. I'li 11 reddish, feet the same atukmli.a. 



b. Tarsus not longer tli:in the middle toe aiul clau . 



' 2. Bill reddish, feet the .sanu- pka.mu.im. 



3. Bill black, feet red or yellow piiii..vi)KU*inA. 



c. Tarsus shorter tliau tiie middle toe without claw. 



4. Wings underneath, dark pluuil)cous minu i us. 



