260 MALACOPTERYGII. — PLEURONECTID^. 
liarity tlian that of being greatly depressed or 
flattened horizontally, like the Skates, which at 
flrst 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 Chaetodons. The 
latter, however, like other fishes, swim with the 
back uppermost, notwithstanding their thinness ; 
but the Turbot 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 
