In connection, however, with this subject, there are two considerations by no means to be lost sight of: Firstly, the extent to which the entire science of ornithology may be regarded as having been derived from European birds; those having been studied, and ornithological science being in some measure an induction from them by the fathers and founders of this branch of Zoology. Secondly, whether in reality the production of the higher developments in birds is not peculiar to the western portions of the two great hemispheres, at least in the northern regions of these divisions of the globe. We regard it as evidently the case in the Old World, and not less so in America. That the ornithology of western North America produces the highest developments of forms in this class of animals that are to be found on this continent, we think fully demonstrable. But at present we regard it as true that Europe produces marked ornithological types of divisions strictly natural. There are about one hundred known species of Swallows, of which eighty-five are in the collection of the Philadelphia Academy. The South American birds of this family, for the greater part, belong to genera represented in North America. Of the genus _Progne_ there are several species peculiar to that portion of this continent, several of which possess habits and manners very similar to those of the Purple Martin. The same may be said of several species of _Acanthylis_, two or three of which considerably resemble our Chimney Bird. Of the Bank Swallows (_Cotyle_), there are also several South American species. III. SUB-FAMILY HALCYONIDÆ. THE KING-FISHERS. General form short, thick, and robust; bill usually long, sharp, and adapted to striking and seizing their prey, which, in the greater part of the species, consists of fishes; wings generally long, and adapted to quick though not long-continued flight; tail usually short; legs short, frequently very strong; toes long, frequently partially joined together and flattened on the soles. Of this extensive family, species are distributed throughout all the temperate and tropical regions of the world, though much more abundant in the latter. Many species habitually frequent the vicinity of the water, and subsist on fishes and small aquatic animals of other classes, but there are birds of this family that are found in the recesses of forests and other comparatively dry localities. Two species only of King-Fishers have as yet been discovered in the United States. I. GENUS CERYLE. Boie, Isis, 1828, p. 312. Form stout and strong; head large; bill long, straight, wide at base, and suddenly compressed to the point, which is sharp; aperture of the nostrils large; wings long; second and third quills usually longest; tail rather short, wide; legs short; tarsi very short; toes moderate, united at their bases, flattened and padded beneath.