740 SYSTEMATIC SYNOPSIS.— L0NGIFENNE8—GAVIM. 



ation rims through nearly all the species : they are white, with a darker mantle (stragulwm)^ 

 and in most cases with black crossing the primaries near the end, the tips of the quills white. 

 The shade of the mantle is very variable in the same species, according to climate, action 

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

 since it is contimuaUy 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 that 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 are found in every stage. They are always da/rher than the old, often 

 quite dusky ; usually with black or ilesh-colored 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 sqaare. 



Head never hooded ; under parts never rosy-tinted ; size medium and large; bill stout. 

 Hallux well developed, witli perfect claw. 



Adult white, with a colored mantle, or dark, with white head Lotus 308 



Adult entirely white ; feet black . . Pagophila 310 



Hallux usually defective. (Tail emarginate in the young) Rissa 309 



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



ChroicocepTmlus 311 



Tail wedge-shaped ; neck collared ; small . , Ehodostethia 312 



Tall forked ; head hooded Xema 313 



308. IjA'RUS. (Grr. Xapoi, laros, Lat. larus, a guU.) Gulls. Bill shorter than the head or 



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



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



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



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



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



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



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



broader 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 longest, second but little shorter, rest rapidly graduated. Tail of moderate length, always 



even, never forked nor rounded. Legs rather slender, of moderate length'; tibise 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 mediuu) 



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 qf Species. 



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



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 



gtavcus 768 



