Though we regard the law of priority as of great importance, we have in the case of this species continued Gmelin’s specific name _fuscus_, (1788,) though it had been previously used by Fabricius, (1780; see _Hierofalco sacer_ in this synopsis.) We know of no practical benefit, however, that would now result from the alteration of this long established name, especially as the _fuscus_ of Fabricius is a synonyme itself. Any naturalist, however, being so moved, may call this bird _Accipiter dubius_, if he chooses, and shall not be molested by us. 2. Accipiter Cooperii. (Bonaparte) Cooper’s Hawk. Falco Cooperii. Bonap. Am. Orn. II. p. 1. (1828.) Falco Stanleii. Aud. Orn. Biog. I. p. 186. (1831.) Bonap. Am. Orn. pl. 1, fig. 1, young. Aud. B. of Am. pl. 36, 141, fig. 3; Oct. ed. I. pl. 24, adult and young. Larger than the preceding; slender; wings short; tail rounded. Adult, head above brownish black, mixed with white on the occiput; other upper parts dark ashy brown, with the shafts of the feathers brownish black; an obscure rufous collar on the neck behind. Throat and under tail-coverts white, the former with lines of dark brown; other under parts transversely barred with light rufous and white; tail, dark cinereous, with four wide bands of brownish black, and tipped with white; quills ashy brown, with darker bands, and white marks on their inner webs. Young. Head and neck behind yellowish white tinged with rufous, and with longitudinal oblong stripes of brown; other upper parts light umber brown, with large partially concealed spots and bars of white; upper tail-coverts tipped with white; under parts white, with narrow longitudinal stripes of light brown; tail as in adult. Dimensions. Female, total length 18 to 20 inches, wing 10 to 11, tail 8½; male, 16 to 17, wing 9½ to 10, tail 8 inches. Hab. The entire territory of the United States. Chili, (Gay.) Spec. in Mus. Acad. Philada. Obs. Rather a difficult species to the ornithologist, on account of the great variations in its colors, and in size also. It is, in fact, unusual to find two alike in a dozen specimens. Very similar when adult to _A. fuscus_, but much larger. The adults of both sexes are the same in color. We have latterly suspected that the smaller specimens usually considered as young males of this bird, are really the young of the species next below, (_A. Mexicanus_.) This bird is of frequent occurrence in the United States. 3. Accipiter Mexicanus. Swainson. The Mexican Black-capped Hawk. Accipiter Mexicanus. Swains. Faun. Bor. Am. Birds p. 45, (1831,) not figured.