254 BRITISH FRESHWATER FISHES 



The Flat-fishes inhabit the seas of all parts of 

 the world, except the polar regions ; some are found 

 in deep water, but the majority prefer sandy shores ; 

 quite a number ascend rivers for some distance, but 

 in our islands only one, the Flounder, constantly 

 occurs in fresh water above tidal limits. 



THE FLOUNDER or FLUKE (Pleuronectes flesus) 

 has the body ovate in form, with the greatest depth 

 nearly one-half the length. The eyes are usually 

 placed on the right side and are separated by a bony 

 keel, which is continued backwards as a smooth or 

 tuberculated postorbital ridge to the origin of the 

 lateral line. The mouth is rather small, terminal, 

 oblique, with the lower jaw a little projecting; the 

 teeth are pointed in the young, but in the adult 

 they are chisel-shaped and arranged in a single 

 series ; on the blind side the jaw-bones are stronger 

 and the teeth more numerous ; for example, in a 

 specimen about a foot long I count on the blind 

 side twenty-two teeth in the upper jaw and the 

 same number in the lower, but on the eyed side 

 only ten upper and thirteen lower teeth. 



The dorsal fin commences above the upper eye 

 and is composed of from fifty-three to sixty-three 

 simple rays, the middle ones being the longest ; 

 the anal is similar, of thirty-seven to forty-five 

 rays, commencing not far behind the pelvics, and 

 preceded by a forwardly directed spine ; the 

 caudal fin is well developed, truncate, borne on a 

 peduncle which is nearly as long as deep ; the 

 pectoral and the six-rayed pelvic fins are equally 

 developed on both sides. The body is covered with 

 small, smooth scales, whilst modified scales in the 



