General form robust; bill, rather short, very strong; tooth, prominent; wing, long, second and third quills longest, and nearly equal; tail, rather long. Female nearly adult. Narrow frontal band; line over the eye, cheeks and entire under parts, white; narrow stripe from the corner of the mouth, dark brown; some feathers on the breast and abdomen, with longitudinal stripes and spots of brown, which color forms a large spot on the flank, plumage on the sides also with spots of brown. Entire plumage of the upper parts, brown, many feathers with rufous edgings; paler on the rump; tail above, grayish brown, with transverse bars of white, and narrowly tipped with the same color. Quills, dark grayish brown, with numerous bars of white on their inner webs; under wing-coverts, dark brown, edge of wing at the shoulder and below, white, spotted with brown. The brown of the back extending somewhat on to the breast at the wing-joint. Bill, bluish horn color, under mandible yellow at its base. Large space around the eye, bare, with a narrow edging of brown on the first plumage encircling it. Younger Female. Entire plumage brownish black, throat white, and many feathers on the under parts with edgings and circular spots of white; under wing-coverts, also, with circular spots of white; under tail-coverts with wide transverse stripes of white. Young Male? Frontal band nearly obsolete; entire upper parts, uniform brown, with narrow rufous stripes on the head; under parts, white, with a tinge of reddish yellow, and nearly every feather with a narrow longitudinal stripe of blackish brown; large spaces on the flanks brown. Tarsi and feet lead colored. Dimensions. Female (of skin), total length about 20 inches, wing 14, tail 8 inches. Hab. Sources of the Platte river, (Dr. Townsend.) California, (Dr. Heermann.) Puget’s Sound, (U. S. Ex. Exp. Vincennes.) Spec. in Mus. Acad. Philada., and in Nat. Mus. Washington. Obs. Very similar, in the two first stages of plumage above described, to _Falco jugger_ of India, (Gray’s Illustrations of Indian Zoology, II. pl. 26, and Jerdon’s Illustrations of Indian Ornithology, pl. 44,) but larger. We have, however, never seen the young of _F. jugger_ in the plumage of the young of our species as described above, from Dr. Heermann’s Californian specimens. This is the first species of this group of Falcons (the Laniers and Juggers) yet discovered in America, and is especially remarkable on account of its near affinity to the Asiatic species. II. GENUS HIEROFALCO. Cuvier, Reg. An. I. p. 312, (1817.)