HABITS. But little is known in regard to the distribution or history of this species. It appears to be peculiar to Arizona and Mexico. There is no good reason to suppose that it differs materially in any of its habits from the other species of this genus. Dr. Cooper, who observed this species at Fort Mojave, states that it is a winter resident of that region in small numbers; and, so far as he observed, is undistinguishable either in habit or general appearance from either of the other species which at that season are also found there. Its cry of alarm resembles that of the common wren. Polioptila melanura, LAWR. BLACK-CAPPED GNATCATCHER. _Culicivora atricapilla_, LAWRENCE, Ann. N. Y. Lyc. V, Sept. 1851, 124 (not of SWAINSON). _Culicivora mexicana_, CASSIN, Illust. I, 1854, 164, pl. xxvii (not of BON.). _Polioptila melanura_, LAWRENCE, Ann. N. Y. Lyc. VI, Dec. 1856, 168.—BAIRD, Birds N. Am. 1858, 382; Review, 68.—HEERMANN, P. R. R. R. vol. X (Williamson), 1859, 39.—COOPER, Birds Cal. 1, 37. SP. CHAR. Above plumbeous-blue. Whole crown, to bill and eyes, with tail, lustrous blue-black. Beneath pale bluish-gray, almost white on chin and anal region; the flanks and crissum tinged with brown. Edge of eyelids, and margin and tip of outer web of first and second lateral tail-feathers, white. Female and young without the black of the crown. Length, 4.15; wing, 1.85; tail, 2.10. HAB. San Diego to Fort Yuma and Cape St. Lucas. Arizona, COUES. Specimens of this species from Cape St. Lucas differ from those of San Diego described in the P. R. R. Report (7,191) in having the whole of the outer web of the outer tail-feather white, and in a rather larger white tip. The colors beneath are a little less ashy, though not of a pure white. The ash of the back is rather lighter and purer. The lores are rather lighter. The first primary is a little larger and broader. It is possible that the restriction of the white of the outer web of the exterior tail-feather to the outer half only is an unusual circumstance, as both Mr. Cassin and Mr. Lawrence, in their descriptions, speak of the entire outer web being white,—the second feather being of the former character. Under these circumstances there will be little specific difference between the tails of _P. melanura_ and _plumbea_. The female birds will then be separated by the light superciliary line and much shorter tarsi of _P. plumbea_,—the latter measuring .63 instead of nearly .70 of an inch.