PLEURONECTIDE, a family of fishes included in Curler's malaeopterygii, but belong.. ing to the order aafiea»thiui of Mfiller's system (see MALAc0FTF.RYGII), and rema•kahla for a character to which there is nothing similar in any other vertebrate animals, a want of symmetry in the and for swimming not with the back uppermost, like other fishes, but with one side upppermost. Thq. 11.111Far structure of the head adapts it to this mode of swimming,, both eyes being on Btat side which is uppermost. Some of the bones of the head are distorted to a very considerable degree, but there is no want of symmetry in those of the body. The sides of the mouth are unequal. The body is extremely compressed, whence the pleuronectithe are popularly termed fiat fish, the back and belly being mere edges fringed by the dorsal and anal fins. The pectoral fins arc generally unequal, also the ventral tins, those of the louver side being smaller than those of the upper. The upper side is often brown, or of some darkish color, and variously marked; the lower side whitish The color of the upper side generally corresponds so much with that of the bottom, close to which these fishes swim, that they readily escape observation; and on this they seem chiefly to depend for safety, although, when hard pressed, they raise themselves in a vertical position, and suddenly throw themselves upward :Ind forward to some distance, but then. resume their ordinary posture, and as
close to the bottom as possible. Their ordinary swimming is by a Idnd of undulating movement. They swim witb.great activity. They have no air-bladder. They abound chiefly where the bottom is smooth, either muddy or sandy. All of them are sea-fishes, but seine arc very common in brackish water, ascend rivers, and can be kept in fresh water ponds. Many of them are in great esteem for the table. The turbot, halibut, brill, plaice, and flounder are examples of this family.