The size and abundance of Flat-fishes, and the flavour of the flesh of the majority of the species, render this family one of the most useful to man; and especially on the coasts of the northern temperate zone, their capture is one of the most important sources of profit to the fishermen.
Psettodes.—Mouth very wide, the maxillary being more than one-half of that of the head. Each jaw armed with two series of long, slender, curved, distant teeth, the front teeth of the inner series of the lower jaw being the longest, and received in a groove before the vomer; vomerine and palatine teeth. The dorsal fin commences on the nape of the neck.
This genus fitly heads the list of Flat-fishes, having retained more of symmetrical structure than the other members of the family, and, therefore, their eyes are as often found on the right as on the left side. It seems to swim, not unfrequently, in a vertical position. Only one species is known, Ps. erumei, common in the Indian Ocean.
Hippoglossus.—Eyes on the right side; mouth wide, the length of the maxillary being one-third of that of the head. Teeth in the upper jaw in a double series; the anterior of the upper jaw and the lateral of the lower strong. The dorsal fin commences above the eye.
The “Holibut” (H. vulgaris) is the largest of all Flat-fishes, attaining to a length of five and six feet, and a weight of several hundredweights. It is found along the northern coasts of Europe, on the coasts of Kamtschatka and California, particularly frequenting banks situated at some distance from the coast, and at a depth of 50 to 120 fathoms.
Other genera, with nearly symmetrical mouth, in which the dorsal fin commences above the eye, are Hippoglossoides (the “Rough Dab”) and Tephritis.
Rhombus.—Eyes on the left side. Mouth wide, the length of the maxillary being more than one-third of that of the head. Each jaw with a band of villiform teeth, without canines; vomerine teeth, none on the palatines. The dorsal fin commences on the snout. Scales none or small.
Seven species from the North Atlantic and Mediterranean, of which the most noteworthy are the “Turbot,” Rh. maximus, one of the most valued food-fishes, and growing to a length of three feet; the “Turbot of the Black Sea,” Rh. mæoticus, the body of which is covered with bony, conical tubercles, which are as large as the eye; the “Brill,” Rh. lævis, represented on the North American coasts by Rh. aquosus; the “Whiff,” or “Mary-sole,” or “Sail-fluke,” Rh. megastoma; “Bloch’s Top-knot,” Rh. punctatus (described by Yarrell as Rh. hirtus, and often confounded with the following species).
Phrynorhombus, differing from Rhombus in lacking vomerine teeth. The scales are very small and spiny.
The “Top-knot” (Ph. unimaculatus) occurs occasionally on the south coast of England, and is more common in the Mediterranean; it is a small species.