260 MALACOPTERYGII. — PLEURONECTID^. 



liarity than that of being greatly depressed or 

 flattened horizontally, like the Skates, which at 

 first sight they much resemble : but, in fact, 

 the coloured surface is not the back, nor the 

 white surface the belly, in the Flat-fish, but these 

 are truly the two sides, right and left, so that 

 instead of being depressed, it is compressed, or 

 flattened vertically, like the Chastodons. The 

 latter, however, like other fishes, swim with the 

 back uppermost, notwithstanding their thinness ; 

 but the Turbo t or Sole, swims or grovels along 

 the bottom, upon its side, the coloured side, right 

 or left, being uppermost. The term Pleuronectes, 

 compounded of two Greek words, signifying side- 

 swimmer, expresses this peculiarity. 



But this is not all. If the eyes had been 

 placed like those of the Chaetodon, for example, 

 one on each side, that which belonged to the 

 white or inferior side, would be rendered useless, 

 since it would be almost perpetually buried in 

 the mud of the bottom. Hence, by an unprece- 

 dented exception to the symmetry which marks 

 the organs of sense in all other vertebrate animals, 

 both of the eyes are placed on the same side of 

 the head, one above the other. They are, how- 

 ever, frequently not in the same line, and one is 

 often smaller and less developed than the other. 



In addition to the above peculiarities, we may 

 mention that the spine makes a sudden twist near 

 the head to one side ; that the bones of the head are 

 not symmetrical ; that the two sides of the mouth 

 are unequal ; that the pectoral and ventral fins 

 of the under side are generally smaller than those 

 of the upper ; and that the dorsal and anal gene- 

 rally correspond to each other, the one fringing 



