Dr. Kennerly, who procured a single specimen of this species while his party was encamped on the Little Colorado, found it busily engaged in seeking its prey among the bushes that grew along the river-bank. It was shy, and was procured with difficulty. Dr. Suckley speaks of this Hawk as not at all rare in Oregon. He procured a specimen of it at Fort Dalles, in the beginning of the winter of 1854–55, which had been killed in the act of carrying off a barn-yard fowl of about its own weight, and which it had just seized near the door of a dwelling-house,—an act demonstrative of a union of courage, ferocity, and strength inferior to none of its congeners. Dr. Cooper characterizes this as one of the shyest of Hawks, as it is also one of the swiftest, flying with rapid flappings of the wings. It seems to prefer the borders of prairies, where it catches hares, quails, and even larger game. Mr. Ridgway informs me that this Hawk was seen by him in Southern Illinois, near Mt. Carmel, September 27, 1871. It had been obtained once before within the limits of Illinois, but in the northwestern part of the State, at Rock Island, by I. Dickenson Sergeant, of Philadelphia, and presented by him to the Academy of Natural Science. Its nest and eggs were taken in Utah by Mr. Ricksecker. I have no notes in regard to the former. A finely marked specimen of one of the eggs procured by him is in my cabinet. It measures 2.15 inches in length by 1.65 in breadth. It is of a somewhat less rounded-oval shape than are the eggs of the _anatum_. The ground-color is a rich cream, with a slightly pinkish tinge, and is beautifully marked with blotches of various sizes, shapes, and shades of a red-brown tinged with chestnut, and with occasional shadings of purplish. These are confluent about one end, which in the specimen before me chances to be the smaller one. It very closely resembles the eggs of the European _F. lanarius_. An egg in the Smithsonian Collection (15,596), taken at Gilmer, Wyoming Territory, May 13, 1870, by Mr. H. R. Durkee, has a ground-color of pinkish-white, varying in two eggs to diluted vinaceous, thickly spotted and minutely freckled with a single shade of a purplish-rufous. In shape they are nearly elliptical, the smaller end being scarcely more pointed than the larger. They measure 2.27 by 1.60 to 1.65 inches. The nest was built on the edge of a cliff. Its eggs were also taken by Dr. Hayden while with Captain Raynolds, at Gros Vent Fork, June 8, 1860. SUBGENUS FALCO, MŒHRING. _Falco_, MŒHRING, 1752. (Type, _Falco peregrinus_, GM. = _F. communis_, GM.) _Rhynchodon_, NITZSCH, 1840. (In part only.) _Euhierax_, WEBB. & BERTH., 1844. (Type, _Falco_—?) _Icthierax_, KAUP, 1844. (Type, _Falco frontalis_, DAUD.) [Illustration: =51293=, ♂. ¼ _F. aurantius._] [Illustration: =52814=, ♀. _F. rufigularis_ (nat. size).] [Illustration: =51293=, ♂. ½ _F. aurantius._] [Illustration: =51293=, ♂. NAT. SIZE. _F. aurantius._]