PRIACANTHUS.--Body short, compressed, covered with small rough scales, which extend also over the short snout. Lower jaw and chin prominent. Eye large. All the teeth villiform, without canines; teeth on the vomer and palatine bones. One dorsal fin with ten spines, anal with three. Præoperculum serrated, with a more or less prominent, flat, triangular spine at the angle. A very natural genus, easily recognised, and without direct relation to the other Percoid genera. The species, of which seventeen are known, are spread over nearly all the tropical seas, and belong to the more common fishes. They scarcely exceed a length of twelve inches, and are very uniformly coloured, red, pink, and silvery prevailing. * * * * * The following three genera form a group by themselves, which, however, is defined rather by its geographical limits and similarity of general appearance than by distinctive anatomical characters. The species are abundant in the fresh waters of the United States, and well known by the name of “Sun Fishes.” They rarely exceed a length of six inches, and are not used as food. The number of species is uncertain. CENTRARCHUS.--Body short, compressed, with scales of moderate size. All the teeth villiform, without canines; teeth on the vomer, palatines, and on the tongue. One dorsal fin; anal generally with more than three spines. Præoperculum without serrature; operculum not lobed. BRYTTUS.--Body short, compressed, with scales of moderate size. All the teeth villiform, without canines; teeth on the vomer and palatine bones. One dorsal fin with nine or ten, anal with three spines. Præoperculum not serrated; operculum with a rounded membranaceous coloured lobe behind. POMOTIS.--Body short, compressed, with scales of moderate length. All the teeth villiform, without canines; teeth on the vomer, but none on the palatine bones. One dorsal, with from nine to eleven spines, anal with three. Præoperculum entire or minutely serrated; operculum with a rounded membranaceous coloured lobe behind. * * * * * A NORTH AMERICAN Freshwater genus, _Aphredoderus_, occupies a perfectly isolated position in the system, and is evidently the type of a distinct family. It resembles the “Sun-fishes” of the same country with regard to the structure of the vertical fins, but has the vent situated in front of the ventrals, which are composed of more than five soft rays. The body is oblong, compressed, covered with ctenoid scales. The dorsal fin is single, and has three spines in front. Infraorbital and præoperculum with spinous teeth. Villiform teeth in the jaws, on the vomer and palatine bones. _A. sayanus_ from the southern streams and fresh waters of the Atlantic States.