Arnoglossus.—Mouth wide, the length of the maxillary being more or not much less than one-third of that of the head. Teeth minute, in a single series in both jaws; vomerine or palatine teeth none. The dorsal fin commences on the snout. Scales of moderate size, deciduous; lateral line with a strong curve above the pectoral. Eyes on the left side.
Seven species from European and Indian Seas. The “Scald-fish” (A. laterna) is common in the Mediterranean, and extends to the south coast of England; it is a small species.
Pseudorhombus.—Mouth wide, the length of the maxillary being more than one-third of that of the head. Teeth in both jaws in a single series, of unequal size; vomerine or palatine teeth none. The dorsal fin commences on the snout. Scales small; lateral line with a strong curve anteriorly. Eyes on the left side. Interorbital space not concave.
A tropical genus with a few outlying species, represented chiefly in the Indo-Pacific, and also in the Atlantic. Seventeen species.
Rhomboidichthys.—Mouth of moderate width or small. Teeth minute, in a single or double series; vomerine or palatine teeth none. Eyes separated by a concave more or less broad space. The dorsal fin commences on the snout. Scales ciliated; lateral line with a strong curve anteriorly. Eyes on the left side.
A tropical genus, but also represented in the Mediterranean and on the coast of Japan. Sixteen species, the majority of which are prettily coloured and ornamented with ocellated spots; in some species the adult males have some of the fin-rays prolonged into filaments.
Other genera with nearly symmetrical mouth, in which the dorsal fin commences before the eye, on the snout, are Citharus, Anticitharus, Brachypleura, Samaris, Psettichthys, Citharichthys, Hemirhombus, Paralichthys, Liopsetta, Lophonectes, Lepidopsetta, and Thysanopsetta.
Pleuronectes.—Cleft of the mouth narrow, with the dentition much more developed on the blind side than on the coloured. Teeth in a single or in a double series, of moderate size; palatine and vomerine teeth none. The dorsal fin commences above the eye. Scales very small or entirely absent. Eyes generally on the right side.
This genus is characteristic of the littoral fauna of the northern temperate zone, a few species ranging to the Arctic circle. Twenty-three species are known, of which the following are the most noteworthy: P. platessa, the “Plaice,” ranging from the coast of France to Iceland; P. glacialis, from the Arctic coasts of North America; P. americanus, the transatlantic representative of the Plaice; P. limanda, the common “Dab;” P. microcephalus, the “Smear-dab;” P. cynoglossus, the “Craig-fluke;” P. flesus, the “Flounder.”
Rhombosolea.—Eyes on the right side, the lower in advance of the upper. Mouth narrower on the right side than on the left; teeth on the blind side only, villiform; palatine and vomerine teeth none. The dorsal fin commences on the foremost part of the snout. Only one ventral which is continuous with the anal. Scales very small, cycloid; lateral line straight.