2602 Bulletin 4.7, United States National Museum. 



Suborder HETEROSOMATA. 

 (THE FLATFISHES.) 



"Cranium posteriorly normal; anteriorly with twisted vertex, to allow 

 2 orbits on the same side, or 1 vertical and 1 lateral; basis cranii not 

 quite simple. Dorsal fin long, of jointed rays; superior pharyngeals 4, 

 the third longest, much extended forward, the inferior separate." (Cope.) 

 This suborder includes the 2 families, Pleuronectidce and Soleidw. Its near- 

 est relationship is probably with the Gadidci', although the developed 

 pseudobranchise and the thoracic ventral fins, indicate an early differentia- 

 tion from the anacanthine fishes. In the very young fishes the 2 sides of 

 the body are alike and the eyes are 1 on each side, with normal cranium. 

 (ETepoc,, different; (j&jua, body.) (Anacanthini pleuronectoidei, Giinther, 

 Cat., iv, 399, 504.) 



FAMILIES OF HETEROSOMATA. 



a. Preopercular margin more or less distinct, not hidden by the skin and scales of the 

 head ; eyes large, well separated ; mouth moderate or large ; teeth present. 



PLEURONECTIDJE, ccxrx. 



aa. Preopercular margin adnate, hidden by the skin and scales of the head; eyes small, 

 close together ; mouth very small, much twisted ; teeth rudimentary or wanting. 



SOLE1DJE, CCXX. 



Family CCXIX. PLEURONECTID^E.* 

 (THE FLOUNDERS.) 



Body strongly compressed, oval or elliptical in outline; head unsym- 

 metrical, the cranium twisted, both eyes being on the same side of 

 the body, which is horizontal in life, the eyed side being uppermost and 

 colored, the blind side lowermost and usually plain. In the very young 

 fish the bones of the head are symmetrical, 1 eye on each side, and the 

 body is vertical in the water. In most species the cranium becomes 

 twisted, bringing the upper eye over with it. Eyes large, well separated. 

 Mouth small or large, the dentition various, the teeth always present; 

 premaxillaries protractile; no supplemental maxillary bone; pseudo- 

 branchiae present. Gills 4, a slit behind the fourth; lower pharyngeals 

 separate ; no air bladder ; preopercle with its margin usually distinct, not 

 wholly adnate or hidden by the skin of the head ; vent not far behind head, 

 the viscera confined to the anterior part of the body. Scales various, 

 rarely absent, usually small. Lateral line usually present, extending on 

 the caudal fin, sometimes duplicated or wanting. Dorsal fin long, con- 

 tinuous, of soft rays only, beginning on the head; anal similar, shorter; 

 caudal various, sometimes coalescent with dorsal and anal; pectorals 

 inserted rather high, rarely wanting ; ventrals under the pectorals, usu- 

 ally of several soft rays, one of them sometimes wanting. Fishes mostly 

 carnivorous, inhabiting sandy bottoms in all seas, some species ascending 

 rivers. Many of them are important food-fishes. Genera about 55 ; species 



* For complete synonymy and descriptions of the American species of this family of 

 fishes, see "A review of the flounders and soles (Pleuronectidce) of America and Europe," 

 by David Starr Jordan and David Kop Goss, in Report United States Fish Comm. for 1886, 

 225-342, pis. 1 to 9, first published in 1889. 



