164 TELEOSTEI : IIETEROSOMATA. — XXI. 



young are symmetrical, one eye on each side, the body is translu- 

 cent and the fish is vertical in the water. Tlie processes by which 

 tlic eye of the lower side becomes transferred throuj^h or over tiie 

 head to the other side are very curious and interesting. There is 

 but one family, {erfpds different ; awna, body.) 



Family LXXXIX. PLEURONECTID^. (The 

 Floim>i;ks.) 



Body strongly compressed, the cranium twisted so that both eyes 

 are on the colored side; mouth and dentition various; premaxil- 

 larics protractile; maxillary simple ; ])seudobranchia3 present. Gills 

 4 ; no air bladder ; vent not far behind head ; scales various ; fins 

 without spines. I), very long ; A. similar, shorter ; P. and V. vari- 

 ous. Fishes mostly carnivorous, chiefly found on sandy sea-bottoms, 

 some of them ascending rivers. Genera 50; species 450. Those 

 species found in Arctic seas have, as usual, an increased numl)er of 

 vertebrae ; the tropical forms have 30 to 35 ; tlie others 40 to 70. 



c. Flounders: Edge of preopercle free; teeth present; P. and V. well developed 

 (witli rare exceptions). 

 b. Mouth nearly symmetrical, the teeth nearly alike on the two sides, the 

 gape usually but not always wide. 

 c. Ventral tins symmetrical, similar in position and in form of base, the 

 ventral of eyed side not extended along the ridge of abdomen. 

 (Ilipjiti^hmiiia;.) 

 d. Vertebnu and fin rays much increased in number (vertebra? about 

 60; D.lOO; A. 85); body elongate; C. lunate; lateral line simple; 

 no anal s])ine; eye on right side. 



e. Lateral line without arch. . . . PLATVSOMATiruTHVS, 226. 

 ee. Lateral line with an arch anteriorly. . . IIiitoolossus. 227. 



dd. Vertebra; and fin rays in moderate number; (Vert, less than 46; 

 D. loss than 95; A. less tiian 75); C. double truncate. 



f. Lateral line without arch; vertebr;e 45; eyes on rit,'lit side; scales 



liiin, ciliated; spine before A. strong; I), begiiuiing above eye. 



HirpoGLossoiDES, 228. 



ff. Lateral line arched in front; vertebrae 35 to 41; eyes on left side; 



scales nearly smooth; anal spine weak; D. beginning before 



eye Pakaliciithys, 229. 



CC. Ventral (ins unsymmetrical, dissimilar in position or in form ; the left 

 V. extended along ridge of abdomen ; eyes on left side. (Pleu- 

 ronecliiue.) 



g. Vomer with teeth; laforal line arched in front; vertebra* 31 to 

 3(5; mouth large; teeth in bands; form broad-ovate; scales 

 cycloid, small or wanting; intcrorbital space not concave. 



I'LKiritONKCTES, 230. 



gg. Vomer toothless; V. free from A; Vert. 34 to 40. 



h. Lateral line arched in front; teeth small, in 1 or 2 series; in- 

 tcrorbital space broad, concave; scales small, ctenoid. 



Platoi'Huys, 231. 



