The Plaice Tribe: Pleuronectinæ.—The plaice tribe pass gradually into the halibut tribe, from which they differ in the small mouth, in which the blunt teeth are mostly on the blind side. The eyes are on the right side, the vertebræ are numerous, and the species live only in the cold seas, none being found in the tropics. In most of the Pacific species the lateral line has an accessory branch along the dorsal fin. The genus Pleuronichthys, or frog-flounders, has the teeth in bands. Pleuronichthys cornutus is common in Japan and three species, Pleuronichthys cœnosus being the most abundant, are found on the coast of California. Closely related to these is the diamond-flounder, Hypsopsetta guttulata of California. Parophrys vetulus is a small flounder of California, so abundant as to have considerable economic value. Lepidopsetta bilineata, larger and rougher, is almost equally common. It is similar to the mud-dab (Limanda limanda) of northern Europe and the rusty-dab (Limanda ferruginea) of New England.
Fig. 438.—Wide mouthed Flounder, Paralichthys dentatus (L.). St. George I., Md.
The plaice, Pleuronectes platessa, is the best known of the European species of this type, being common in most parts of Europe and valued as food. Closely related to the plaice is a second species of southern Europe also of small size, Flesus flesus, to which the name flounder is in England especially applied. The common winter flounder of New England, Pseudopleuronectes americanus, is also very much like the plaice, but with more uniform scales. It is an important food-fish, the most abundant of the family about Cape Cod. The eel-back flounder, Liopsetta putnami, also of New England, is frequently seen in the markets. The males of this species have scattered rough scales, while the females are smooth. The great starry flounder of Alaska, Platichthys stellatus, is the largest of the small-mouthed flounders and in its region the most abundant. On the Pacific coast from Monterey to Alaska and across to northern Japan it constitutes half the catch of flounders. The body is covered with rough scattered scales, the fins are barred with black. It reaches a weight of twenty pounds. Living in shallow waters, it ascends all the larger rivers.
An allied species in Japan is Kareius bicoloratus, with scattered scales. Clidoderma asperrimum, also of northern Japan, has the body covered with series of warts.
Fig. 439.—Eel-back Flounder, Liopsetta putnami (Gill). Salem, Mass.
In deeper water are found the elongate forms known as smear-dab and flukes. The smear-dab of Europe (Microstomus kitt) is rather common in deep water. Its skin is very slimy, but the flesh is excellent. The same is true of the slippery sole, Microstomus pacificus, of California and Alaska, and of other species found in Japan. Glyptocephalus cynoglossus, the craig-fluke, or pole-flounder, of the North Atlantic, is taken in great numbers in rather deep water on both coasts. Its flesh is much like that of the sole. A similar species (Glyptocephalus zachirus) with a very long pectoral on the right scale is found in California, and Microstomus kitaharæ in Japan.
The Soles: Soleidæ.—The soles (Soleidæ) are degraded flounders, the typical forms bearing a close relation to the plaice tribe, from which they may be derived. There are three very different groups or tribes of soles, and some writers have thought that these are independently derived from different groups of flounders. This fact has been urged as an argument against the recognition of the Soleidæ as a family separate from the flounders. If clearly proved, the soles should either be joined with the flounders in one family or else they should be divided into two or three, according to their supposed origin.
The soles as a whole differ from the flounders in having the bones of the head obscurely outlined, their edges covered by scales. The gill-openings are much reduced, the eyes small and close together, the ventral fins often much reduced, and sometimes the pectoral or caudal also. The mouth is very small, much twisted, and with few teeth.