Of this family of birds, the only species that have been ascertained or supposed by naturalists to inhabit that part of North America within our limits, are given in the preceding pages. The group is, however, represented in South America not only by other species of the genera above given, but by various other genera and species, amongst which are some curious and interesting forms. The genus _Steatornis_, containing a single species, first brought to notice by the celebrated Humboldt (_Steatornis caripensis_, Humboldt), is remarkable for its near approach to the Owls, and would, to a casual observer, scarcely be regarded as belonging to any other than that family. The genus _Nyctibius_, which is also South American, contains some species as large as the Crow of the United States, and which are amongst the largest birds of this group. Another genus, _Hydropsalis_, or the Scissors-tailed Goatsuckers, as they are termed by Azara (an enthusiastic and accurate Spanish writer on South American Natural History), are remarkable for having tails of singular forms, and of great length in some species. _Hydropsalis torquatus_ has the two outermost feathers of its tail long, and the two middle feathers also long, leaving the intermediate comparatively short. _Hydropsalis lyra_, Bonaparte, has the outermost feathers of the tail very long, and curved inwards at their ends. Two species, first described by us, _Hydropsalis limbatus_ and _segmentatus_ (in Proc. Acad., Philadelphia), have that appendage several times the length of their bodies. About thirty-five species of _Caprimulgidæ_ inhabit South and Central America and Mexico. The largest birds of this group are natives of Australia. We are inclined to the opinion that this family (and the Swallows also) properly belong to the circle of rapacious birds in which they have been arranged by Prof. Reichenbach, in Avium Systema Naturale (Dresden and Leipsic, 1850).[4] II. FAMILY HIRUNDINIDÆ. THE SWALLOWS. Plumage compact; size generally small; bill small, much depressed, very wide at base, and suddenly compressed to the tip, giving it a somewhat triangular shape; wings long; tail various, frequently forked; legs and feet short and weak. These birds form a peculiar and easily-recognized family, species of which inhabit all parts of the world, and in civilized countries are generally regarded with favor. The Swallows are eminently social and gregarious, being almost constantly seen in companies even in the breeding season, and are amongst the comparatively few birds whose numbers are not diminished by the progress of the settlement and cultivation of countries. They subsist exclusively on insects captured on the wing, in the pursuit of which they exhibit extraordinary powers of flight. A. 1. Genus Hirundo. Linn., Syst. Nat. I. p. 343. (1766.)