554 FISHES. 



upper side, others hold that, as soon as the body of the fish 

 commences to rest on one side only, the eye of that side, in 

 its tendency to turn towards the light, carries the surround- 

 ing parts of the head with it ; in fact, the wdiole of the fore- 

 part of the head is twisted towards the coloured side, which is 

 a process of but little difficulty as long as the framework of 

 the head is still cartilaginous. 



Flat-fishes wdien adult live always on the bottom, and 

 swim with an undulating motion of their body. Sometimes 

 they rise to the surface ; they prefer sandy bottom, and do 

 not descend to any considerable depth. They occur in all 

 seas, except in the highest latitudes and on rocky, jDrecipi- 

 tous coasts, becoming most numerous towards the equator; 

 those of the largest size occur in the temperate zone. Some 

 enter fresh water freely, and others have become entirely 

 acclimatised in ponds and rivers. All are carnivorous. 



Flat-fishes were not abundant in the tertiary epoch ; the 

 only representative known is a species of Bliomhus from 

 Monte Bolca. 



The size and aljundance of Flat-fishes, and the flavour of 

 the flesh of the majority of the species, render this family one 

 of the most useful to man ; and especially on the coasts of 

 the northern temperate zone, their capture is one of the most 

 important sources of profit to the fishermen. 



PsETTODES. — Mouth very wide, the maxillary being more 

 than one-half of that of the head. Each jaw armed with two 

 series of long, slender, curved, distant teeth, the front teeth of 

 the inner seiies of the lower jaw being the longest, and received 

 in a groove before the vomer ; vomerine and palatine teeth. 

 The dorsal fin commences on the nape of the neck. 



This genus fitly heads the list of Flat-fishes, having 

 retained more of symmetrical structure than the other mem- 

 bers of the family, and, therefore, their eyes are as often found 

 on the right as on the left side. It seems to swim, not un- 



