FAMILY PLANIDiE. 293 



This is an exceedingly rare but distinct species. It occurs from the coast of New-York to 

 the gulf of St. Lawrence. 



The Gadus tenuis of Mitchill (Tr. Lit. and Phil. Soc. p. 372), is a Phycis. and if the 

 radial formula be correct, anew species. It is fifteen inches long; brownish back and sides. 

 D. 11.54; P. 16; V. 2; A. 44 ; C. 25. 



FAMILY PLANID&. 



Body flat, compressed vertically. Upper surface dusky, and of various colors ; beneath 

 white. Dorsal single, extending the whole length of the back. Both eyes placed on the 

 same side of the head. $0 air-bladder. Branchial rays six. 



Obs. This family, which comprises about one hundred and thirty species, is well charac- 

 terized. In the want of symmetry in the head, it stands alone among the vertebrated ani- 

 mals ; the eyes being both on the same side of the head, one usually above the other, and often 

 unequal in size. This want of symmetry extends to the mouth, and often to the pectoral fins. 

 In the exceptions, the eyes are placed on a different side from their usual situations, and are 

 then termed reversed individuals ; more rarely it happens that both sides are colored, when 

 they are said to be doubled* The terms right and left, or dextral and sinistral, have been 

 variously applied ; and some confusion has also arisen from the fact, that in transferring the 

 drawings of these fishes to copper, the true position of the sides has been reversed, and the 

 figure and description at variance. The rule proposed by Bloch, is to place the fish on its 

 edge, with the tail to the observer, and the dorsal fin uppermost ; the fish is then said to be 

 dextral or sinistral, according as the colored side is on the right or left hand. 



We have on our coast examples of the following generic groups : Platessa, Hippoglossus . 



* Thus the P. melanognster, Mitchill, is a doubled variety of P. dentaius. 



