Central tail-feathers projecting six inches or more; gradually tapering from the base; the tips acute: tarsus one inch six lines; slightly rugose.
L. parasiticus, Tertnn. Man. d'Orn. torn. ii. p. 796. Faun. Bar. Amer. vol. ii. p. 430. Parasitic Gull, Gould, Europ. Birds, part iv.
Entire length twenty-one inches: length of the bill one inch and six-eighths; of the tarsus one inch six lines; of the central tail-feathers twelve inches; of the wing eleven inches nine lines. Gould*.
Extremely similar to the last species, from which it is principally distinguished by its smaller size, longer central tail-feathers, and shorter tarsi. (Adult male and female). "Top of the head, and the space between the bill and the eyes, of a deep blackish brown, terminating at the occiput; the whole of the upper surface of a clear brownish gray; quills and tail-feathers much darker; the throat, neck, and under surface, of a pure white, with the exception of the cheeks and sides of the neck, which are tinged with a delicate straw-yellow; legs and feet black. The young resemble in colouring the other species of the genus of the same age." Gould.
Apparently of rare occurrence in this country; nor is it known whether it ever breeds with us like the last species. A British-killed specimen is in the British Museum, but I am ignorant from what locality it was obtained. According to Mr. Thompson, it has repeatedly occurred in the Bays of Dublin and Belfast. It is possible that the Arctic Gull noticed by Montagu in the Supplement to his " Ornithological Dictionary," may have been of this species, but in all other cases the bird described under that name by English authors is referable to the L. Richardsonii. According to Mr. Gould, the present species inhabits the shores of the Baltic, the rugged coasts of Norway, and the Polar Regions. Habits similar to those of the rest of the genus.
* The following are the dimensions of a British specimen, in the British Museum, as given in the Faun. Bor. Amer. by Dr. Richardson. "Length, total, twenty inches; the same, excluding central tail-feathers, fourteen inches; of central pair eleven inches; of wing eleven inches six lines; of bill above one inch; of bill to rictus one inch seven lines and a half; of tarsus one inch seven lines; of middle toe one inch three lines; of hind toe two lines; of hind nail two lines; transverse diameter of the bill at the front four lines".