Bill shorter than the head, robust, compressed, higher near the end than at the base. Upper mandible with the dorsal line nearly straight at the base, declinate and arched towards the end, the ridge convex, the sides slightly convex, the edges sharp, inflected, arcuato-declinate towards the end, the tip rather obtuse. Nasal groove rather long and narrow; nostril in its fore part, lateral, longitudinal, linear oblong, wider anteriorly, pervious. Lower mandible with the angle long and narrow, the outline of the crura curved, the dorsal line beyond the prominence slightly concave, the sides erect and nearly flat, the edges sharp and inflected.
Head rather large, oblong, narrowed anteriorly. Neck of moderate length, strong. Body full. Feet of moderate length, rather slender; tibia bare below; tarsus somewhat compressed, covered anteriorly with numerous scutella, laterally with angular scales, behind with numerous small rectangular scales; hind toe very small and elevated, the fore toes of moderate length, rather slender, the fourth longer than the second, the third longest, all scutellate above, and connected by reticulated entire membranes, the lateral toes margined externally with a thick narrow membrane. Claws small, slightly arched, depressed, rounded, that of the middle toe with an expanded thin inner margin.
The plumage in general is close, full, elastic, very soft and blended, on the back rather compact. Wings very long, broad, acute, the first and second quills nearly equal, the rest of the primaries rather rapidly graduated; secondaries broad and rounded, the inner narrower. Tail of moderate length, even, of twelve rounded feathers.
Bill gamboge-yellow, with a large orange-red patch inclining to carmine towards the end of the lower mandible. Edges of eyelids gamboge; iris silvery white. Feet flesh-coloured; claws brownish-black. The head, neck, lower parts, rump and tail, are pure white; the back and wings pearl-grey or light bluish-grey, very slightly tinged with purple; the edges of the wing and the extremities of all the quills, are white. The first six quills are brownish-black towards the end, that colour including the outer webs and the greater part of the inner of the two first, and on the rest gradually diminishing, so as on the sixth merely to form a bar; first quill with a patch of white about an inch and a half long on both webs near the end; second with a circular white patch on the inner web, the tips of all white.
Length to end of tail 23 inches, to end of wings 24 1/2, to end of claws 21 1/2; extent of wings 53; wing from flexure 18; tail 7 1/4; bill along the ridge 2 1/2, along the edge of lower mandible 3; its depth at the angle 3/4; tarsus 2 1/2; middle toe 2 1/4, its claw 4 1/2/12. Weight 1 lb. 10 oz.
The Female is similar to the male, but somewhat less.
Young in November. Plate CCXCI. Fig. 2.
Bill brownish-black, paler at the base of the lower mandible. Edges of eyelids greenish-grey; iris hazel. Feet purplish flesh-colour; claws brownish-black. The general colour of the whole plumage is light purplish-grey, the upper part of the head darker, the lower parts minutely mottled with pale yellowish-grey; the feathers of the upper parts, and the upper tail-coverts, irregularly edged and barred with greyish-white. Primary quills greyish-brown, their inner webs paler, their tips whitish; tail of the same colour, its base and outer webs of lateral feathers irregularly mottled with whitish, the tips brownish-white.
Length to end of tail 18 3/4 inches, to end of wings 20; extent of wings 51; wing from flexure 16; tail 6; bill along the ridge 2, along the edge of lower mandible 2 1/2; tarsus 2 1/4; middle toe 2, its claw 4 1/2/12. Weight 22 oz.
From the examination of individuals of this species, it would appear that little reliance can be placed on the markings of the quills as affording a specific character. Four undoubted specimens of Larus argentatus now before me, have a white spot, varying in length from one to two inches, and including both webs, near the end of the first quill. One has no spot on the second quill; another has a spot on both webs of the second quill of one wing, and a smaller spot on part of the inner web of the same quill of the other wing; the third has a very small spot on part of the inner web of the same quill of both wings; the fourth has a large circular spot on the inner web of that quill also in both wings.