FLAT-FISHES. 553 



Atelcopus from Japan and Xenocephalus from New Ire- 

 land are genera belonging to the Gadoid Anacanths, but are 

 very imperfectly known. 



Second Division — Anacanthini Pleukonectoidei. 



Head and ixirf of the hody unsymmdrically formed. 

 This division consists of one family only : 



PLEUEONECTIDiE. 



The fishes of this family are called " Flat-fishes," from their 

 strongly compressed, high, and flat body; in consequence of the 

 absence of an air-bladder, and of the structure of their paired 

 fins, they are unable to maintain their body in a vertical posi- 

 tion, resting and moving on one side of the body only. The side 

 turned towards the bottom is sometimes the left, sometimes 

 the right, colourless, and termed the " blind " side ; that 

 turned uj)wards and towards the light is variously, and in 

 some tropical species even vividly, coloured. Both eyes are 

 on the coloured side, on which side also the muscles are more 

 strongly developed. The dorsal and anal fins are exceedingly 

 long, without division. All the Flat-fishes undergo remark- 

 able changes with age, which, however, are very imperfectly 

 known and not yet fully understood, from the difficulty of 

 referring larval forms to their respective parents. The larvse 

 are, smgularly enough, much more frequently met in the open 

 ocean than near the coast ; they are transparent, like LejM- 

 cephali ; perfectly symmetrical, with an eye on each side of 

 the head, and swim in a vertical position like other fishes. 

 The manner in which one eye is transferred from the blind 

 to the coloured side is subject to discussion. Whilst some 

 naturalists believe that the eye turning round its axis pushes 

 its way through the yielding bones from the blind to the 



