Dr. Heermann found the extensive marshes of Suisun, Napa, and Sacramento Valleys the favorite resorts of these birds, especially during the winter, and there they seemed to find a plentiful supply of insects and mice. They ranged over their feeding-grounds in small flocks from a single pair up to six or seven. He fell in with an isolated couple in the mountains between Elizabeth Lake and Williamson’s Pass, hovering over a small freshwater marsh. In July and August the young were quite abundant, from which Dr. Heermann inferred that it does not migrate for the purposes of incubation. Dr. Gambel, who procured his specimens at the Mission of St. John, near Monterey, describes it as flying low and circling over the plains in the manner of a _Circus_, and as feeding on the small birds. It was easy of approach when perched on trees, and uttered a loud shrill cry when wounded, and fought viciously. Lieutenant Gilliss, who found them in Chile, describes the nest as composed of small sticks, and states that the number of the eggs is from four to six, and that they are of a dirty yellowish-white with brownish spots. The common name of this Hawk in Chile is _Bailarin_ (from the verb _bailar_, to dance or balance), from the graceful and easy manner in which it seems almost to float upward or to sink in the air. An egg of this species, in the collection of the Boston Society of Natural History, measures 1.64 inches in length by 1.48 in breadth. In shape it is very nearly spherical, and equally obtuse at either end. The ground-color, though nowhere very distinctly apparent, appears to be of a dull white, strongly tinged with a reddish hue. Distributed over the entire egg are broad deep flashes of a dark mahogany-brown, intermingled with others of a similar color, but lighter in shading. These cover the egg more or less completely, in the greater portion of its surface. This egg was taken near Fort Arbuckle, Indian Territory, May 9, 1861, by J. H. Clark, Esq., and sent to the Smithsonian Institution. GENUS ICTINIA, VIEILLOT. _Ictinia_, VIEILL. 1816. (Type, _Falco mississippiensis_, WILSON.) _Nertus_, BOIE, 1826. (Type, _Falco plumbea_, GMELIN.) _Pœcilopteryx_, KAUP, 1844. (Same type.) [Illustration: ♂ =1485=, R. R. ½ _Ictinia mississippiensis._] [Illustration: ♂ =1486=, R. R. ¼ _Ictinia mississippiensis._] [Illustration: =32974=, ♀. ½ =32974=, ♀. ½ =32974=, ♀. ¼ _I. plumbea._]