The Falconidce, according to Mr. Ridgway, may be logically and advantageously divided into four subfamilies, the Falconince or true Falcons, the Polyborince or Caracaras, the Micrasturince or the Tropical Goshawks, and the Her petotherince or Laughing Falcons. The first three of these subfamilies are grouped together on the ground that the posterior toe is abbreviated, being very much shorter than the lateral pair, while the tarsi and toes are covered with small hexagonal scales which are larger in front. In the fourth subfamily (Herpetotherince) the posterior toe is elongated, in fact almost equaling the lateral pair, and the tarsi and toes are covered with uniformly thin, rough, imbricated scales. The Falconince and Polyborince agree in having the nostril a small, round or oblique opening, with a bony-rimmed margin and central tubercle, while in the Micrasturince the nostril is a large opening without either the bony-rimmed margin or central tubercle. In the Falconince the upper tomium is provided with a conspicuous tooth and the lower with a corresponding notch, and one or two of the outer primaries have their inner webs emarginated near their tips. The Polyborince, on the other hand, have the tomia without tooth or notch, and three or more of the outer primaries with the inner webs emarginated or sinuate near the middle portion.
Falcons. We may appropriately begin the consideration of the first sub-family with the true Falcons, which form a very large group of nearly world-wide distribution. Ornithologists are not agreed as to the generic limits within the groups of Falcons, some placing them all in the genus Falco, which is the treatment here adopted, while others have separated them into several, of course closely related, genera. They are mostly medium-sized or large birds of stout, compact build and active habits. They have long, pointed wings in which never more than two primaries are emarginated. The middle toe is usually very long, never much shorter and sometimes longer than the tarsus, which is never with a single continuous row of transverse plates, either in front or behind. The bill is strong, broad at base, and the upper mandible provided with a very prominent notch and tooth.