THE FLAT-FISHES 217 



Pleuronectidae 



I. — Group in which the Teeth are Largest on 

 THE Lower Side 



The Plaice [Pleuronectes flatessa) is an almost solitary 

 exception to the general rule of a familiar fish on all parts 

 of our coasts having a great variety of local names. Another 

 of the genus, the lemon sole, goes by a different name at 

 almost every port ; but a plaice is a plaice in localities hundreds 

 of miles apart. Certainly the fish is an unmistakable form, 

 since its orange-red spots are not found in any other flat-fish 

 of our seas. The head has an even more twisted appearance 

 than that of most flat-fishes ; the eyes are in line and on 

 the right side, separated by a bony ridge. In all flat-fishes 

 the eyes lie just above the sand when their owners are at 

 rest, and to Holt is due the credit of discovering and describing 

 a sac-like membrane, the use of which is to regulate the 

 vertical movements of the eye. Such an apparatus must 

 obviously be of great use to animals that pass a great portion 

 of their existence under these conditions, and the discoverer 

 not unreasonably looked for a similar arrangement in the 

 weevers, which also lie with their eyes just above the sand, 

 but the search was not successful.* The scales of the 

 plaice, which extend to the face, are very small, so that a 

 newly caught plaice feels slimy when handled. The lateral 

 line is nearly straight, with only a slight curve over the 

 pectoral fin. 



In colour the plaice is deep brown, with the afore- 

 mentioned orange-red spots on the right side ; the left, 

 or lower, side is pure white. Further, this white side is 

 perfectly flat, whereas the coloured side is convex. A sharp 

 spine points forward just before the anal fin. The dorsal 

 fin starts above the eyes. The cleft of the mouth is narrow ; 

 the teeth are broad and somewhat blunt, largest on the white 

 * See Proc. Zool. Soc, 1894, p. 431. 



