740 SYSTE3IA TIC SYNOPSIS. — L ONGIPENNES — GA VI^. 



ation runs through nearly all the species: they are w/iiie, with a darker uiautle (sirar/M^Mm), 

 and in must cases with hlack crossing the primaries near the end, the tips of the quills white. 

 The shade of tlie mantle is very variable iu the same species, according t(5 climate, action 

 of the sun, friction, and, other causes ; the pattern of the black on the riuills is still more so, 

 since it is continualhj changing with age, at least until a final stage is reached. Incredible 

 as it may appear, species and even genera have been based upon such shadowy characters. 

 One group of species has the head enveloped in a dark hood in the breeding season, the under 

 parts tinted with peach-blossom hue. The sexes are always alike ; the moult appears to be 

 twice a year, so tliat a winter plumage more or less different from that of summer results ; 

 while the young are never like the old. The change is slow, generally requiring 2-3 years ; 

 in the interim, birds arc found in every stage. They are always darlcer than the old, often 

 quite dusky ; usually with black or flesh-cohired bill ; and if with black on the primaries 

 when adult, the young usually have these quills all black. There being no peculiar extra- 

 limital species, those of our country give a perfect idea of the whole group. Some 75 species 

 are current ; there are certainly not over 50 good ones. 



Analysis of Genera. 

 Tail square. 



Head never hooileil ; under jiarts never rosy-tinted ; size medium and large; bill stout. 

 Hallux well developed, with jierfect claw. 



Adult W'hite, witli a colored mantle, or dark, witli wbite bead Lams 308 



Adult entirely wliite; feet black - PagophUa 310 



Hallu.v usually defective. (Tail emarginate in the yomig) Iiissa 309 



Head in summer hooded, and under parts rosy-tinted; size medium and small; bill slender 



Chro'icocephahis 311 



Tail wedge-shaped; neck collared ; small Hhodostethia 312 



Tail forked ; head hooded Xema 313 



308. LA'RUS. (Gr. Xdpos, laws, Lat. larus, a gull.) GuLLS. Bill shoiter than the head or 

 tarsus, large, strong, more or less robust, usually very stout, deep at the base, higher than 

 broad, compressed througliout, the apex not very acute and never much attenuated or decurved. 

 Culmeu about straight to beyond the nostrils, then convex, the amount of curvature increasing 

 toward the end, varying in different species. Counnissure slightly sinuate at its extreme base, 

 then about straight to near the end, where it is more or less arcuato-declinate. Emineutia 

 symphysis always large, prominent, ;md well-defined, rather obtuse, seldom acute. Nostrils 

 placed rather far forward iu a "well-defined nasal fossa, lateral, longitudinal, pervious, rather 

 bi'iiader anteriorly than posteriorly. Feathers of forehead extending considerably farther on 

 the sides of the upper mandible than on its culmen, but falling considerably short of the 

 nostrils. "Wings when folded reaching beyond the tail, the remiges strong, not very acute, 

 first loneest, second but little shorter, rest rapidly graduated. Tail of moderate length, ahvays 

 even, never forked nor rounded. Legs rather slender, of moderate length ; tibiae bare for a 

 considerable distance above the joint, the naked part smooth. Tarsi about equal to or a little 

 longer than the middle toe and claw, varying but slightly in proportions among the different 

 species ; anteriorly scuteUate, posteriorly and laterally reticulate. Hallux fully developed 

 and always present. Anterior claws stout, strong, little curved, rather obtuse, the inner edge 

 of the middle one dilated. Webs full and broad, scarcely incised. Of very large or medium 

 size, never very small. Robust and powerful. Comprising the largest species of the subfamily 

 and those typical of it. White, with a darker mantle, without a hood ; the head and neck in 

 winter streaked with dusky ; one species dark with white head and red biU. 



Analysis of Species. 



I. Tail and under parts white in adult ; bill and feet not reddish. (Larus. ) 



A Large and robust : mantle whitish or pale pearly ; no black on primaries at any age. 

 Mantle very pale ; primaries the same, fading insensibly into white far from the tips. 



Larger: length about 30.00 inches; wing 18.00 or more; bill and tarsus, each, about 3.00 



glaucus 768 



