Size medium; head rather large; face partially encircled by a ring or ruff of short projecting feathers (as in the Owls). Bill rather short, compressed, curved from the base; nostrils large; wings long, pointed; tail long, wide; tarsi long and slender, compressed; toes moderate; claws long, rather slender. Embraces about fifteen species, of all parts of the world. 1. Circus hudsonius. (Linn.) The Marsh Hawk. The Harrier. Falco hudsonius. Linn., Syst. Nat., I. p. 128. (1766.) Falco uliginosus. Gm., Syst. Nat., I. p. 278. (1788.) Falco europogistus. Daudin, Traité, II. p. 110. (1800.) “Falco uliginosus.” Wilson, Am. Orn., VI. p. 67. “Falco cyaneus. Linn.” Aud., Orn. Biog., IV. p. 396. Edw., Birds, VI. pl. 291; Vieill., Ois. d’Am., pl. 9; Wilson, Am. Orn., VI. pl. 51, fig. 2; Bonap., Am. Orn., II. pl. 12; Aud., B. of Am., pl. 356, oct. ed. I. pl. 26; Faun. Bor. Am., Birds, pl. 29; De Kay, Nat. Hist. N. Y. Orn., pl. 3, figs. 6, 7. Form slender; tarsi long; ruff very distinct on the neck in front. Adult. Upper-parts, head, and breast, pale grayish-cinereous, generally more or less tinged with fuscous, and on the back of the head mixed with dark fulvous; upper tail-coverts white. Under-parts white, usually with many small cordate or hastate spots of light-ferruginous; quills brownish-black, with their outer webs tinged with ashy, and a large portion of their inner webs white; tail light-cinereous, nearly white on the inner webs of the feathers, and with obscure bands of brown; under-surface white; inferior wing-coverts white; secondaries tipped with dark-brown. Young. Entire upper-parts dark umber-brown, mixed with fulvous, and white on the occiput and neck behind; upper tail-coverts white. Tail reddish-brown, with about three broad bands of dark-fulvous, paler on their inner webs. Under-parts rufous, with stripes of brown on the breast and sides; tarsi and feet yellow. In younger birds, on the under-parts the brown stripes are more numerous. Dimensions. _Female_—total length, 19½ to 21 inches; wing, 15½; tail, 10 inches. _Male_—total length, 16 to 18 inches; wing, about 14; tail 8½ to 9 inches. Hab. All of North America; California (Col. M‘Call); Oregon (U. S. Ex. Exp. Vincennes); Cuba (M. de Sagra, M. Lembeye). Spec. in Mus. Acad., Philada. Obs. Resembles to some extent the _Circus cyaneus_ of Europe, but is easily distinguished from it by its colors and rather larger size. The adults and young of this species present great differences in color and general appearance. V. SUB-FAMILY AQUILINÆ. THE EAGLES. Size usually large. Bill large, compressed, straight at base, curved and acute at the tip; wings long, pointed; tail ample, generally rounded at the end; tarsi moderate or rather long, strong; toes long, strong; claws very strong, curved, acute. This sub-family includes about seventy species, of all countries.