164 TELEOSTEI: HETEROSOMATA. XXI. 



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

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

 the eye of the lower side becomes transferred through or over the 

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

 but one family, (erepds different ; cro>/ia, body.) 



FAMILY LXXXIX. PLEURONECTID^l. (THE 

 FLOUNDERS.) 



Body strongly compressed, the cranium twisted so that both eyes 

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

 laries protractile ; maxillary simple ; pseudobranchise present. Gills 

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

 without spines. D. 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 number of 

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



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



(with rare exceptions). 

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



gape usually but not always wide. 



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

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

 (Hippo ylossince.) 



d. Vertebrae and fin rays much increased in number (vertebrae about 

 50; D. 100; A. 85); body elongate; C. lunate; lateral line simple; 

 no anal spine ; eye on right side. 



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

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



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

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



f. Lateral line without arch ; vertebra? 45 ; eyes on right side ; scales 



firm, ciliated; spine before A. strong; D. beginning above eye. 



HIPPOGLOSSOIDES, 228. 



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

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



eye PARALICHTHYS, 229. 



cc. Ventral fins unsymmetrical, dissimilar in position or in form ; the left 

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

 ronectince.) 



g. Vomer with teeth; lateral line arched in front; vertebrae 31 to 

 36; mouth large; teeth in bands; form broad-ovate; scales 

 cycloid, small or wanting; interorbital space not concave. 



PLEURONECTES, 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- 

 terorbital space broad, concave ; scales small, ctenoid. 



PLATOPHRYS, 231. 



