808. 
740 SYSTEMATIC SYNOPSIS. — LONGIPENNES — GAVIZE. 
ation runs through nearly all the species: they are whdte, with a darker mantle (stragulum), 
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 continually 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 differeut 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 darker than the old, often 
quite dusky; usually with black or flesh-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. i 
Tail square. 
Head never hooded; under parts never rosy-tinted; size medium and large; bill stout. 
Hallux well developed, with perfect claw. 
\ Adult white, with a colored mantle, or dark, with white head . . 2 » . + . Larus 308 
Adult entirely white; feet black . : page » « «Pagophila 310 
Hallux usually defective. (Tail emarginate in the young) . a » . . Rissa 309 
Head in summer hooded, and under parts rosy- tinted; size medium and small; bill slender 
Chroitcocephalus 311 
Tail wedge-shaped; neck collared ; small a 3 re « » 1. . « . « Rhodostethia 312 
Tail forked; head hooded . ‘ » . . Xema 818 
LA'RUS. (Gr. Adpos, laros, Lat. nee a gull.) Gone Bill ‘shorts: 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-declinate. 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 ; tibia bare fora 
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 seutellate, 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 bill. 
Analysis of Species. 
I, Tail and under parts white in adult; bill and feet not reddish. (Zarus.) 
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 168 
