Smaller than the preceding, but very similar to it in form and general appearance; wings very long, exceeding the tail, which is short; exserted spines of the tail-feathers sharp, slender, and not so rigid as in the preceding species; tarsi and toes rather slender, naked; plumage above fuliginous brown, lighter on the rump and upper tail-coverts, darker, and tinged with greenish on the head and back; quills dark fuliginous, with a greenish lustre; tail lighter fuliginous; under-parts pale fuliginous, nearly white on the throat, darkest on the abdomen; shafts and spines of the tail-feathers black; bill and feet dark. Dimensions. Total length of skin, sex unknown, 4¼ inches; wing, 4½; tail, 1½ inches. Hab. Columbia River, Oregon (Dr. Townsend). This species, though apparently totally distinct from the common Chimney bird of the United States, has never been noticed since its discovery by Dr. Townsend. It is probably a bird exclusively inhabiting the countries west of the Rocky Mountains. The original specimen brought by Dr. Townsend remains unique in the collection of the Philadelphia Academy. The name of this species was given in honor of Mr. William S. Vaux, of this city, and is a just compliment to one of the most active and valuable members of the Academy. B. OBSCURE AND DOUBTFUL SPECIES OF THIS FAMILY. 1. Hirundo unalaschkensis. Gm., Syst. Nat. I. p. 1025. (1788.) Hirundo aoonalaschkensis. Lath., Ind. Orn., II. p. 577. (1790.) Originally described by Latham from a specimen in the Leverian Museum, as follows:— “Length four inches and a half; bill very short, dusky; the plumage above dull black, without gloss; beneath and sides of the head dusky ash color, the last darkest; rump dirty white; tail forked, each feather round at the end; legs dusky. Inhabits Aoonalashka.” Gm., Syn. II. p. 571. This species is unknown to ornithologists of the present day, and from the above description and the evident similarity of the bird to other small species of this family, would not be recognized without difficulty, unless obtained in the locality as given. It appears to belong to the genus _Collocalia_, Gray, a very remarkable group of small Swallows, that inhabit caves, and are found in several islands in the Pacific Ocean. A species of this genus is the Esculent Swallow of authors (_Collocalia esculenta_), the nests of which are so highly esteemed as an article of food by the Chinese, and are the principal constituent in the somewhat celebrated “Bird’s-nest soup,” a prominent feature in Chinese entertainments. It is probable, too, that the nests of other species of these birds are used for the same purpose. No species of the genus alluded to has been discovered on the continent of America, nor in either of the American islands, except the above. 2. Hirundo phenicephala. Rafinesque, Annals of Nature, p. 4. (Lexington, Kentucky, 1820.)