230 CLASSIFICATION OF FISHES. 



(205.) The second, or sub-typical group, are the 

 Pleuronectidce, or flat fish. These are at once recog- 

 nised by their remarkably flattened bodies, of an oblong 

 or rhomboid shape : the circumference is almost com- 

 pletely margined by the dorsal and anal fins, the rays of 

 which are, for the most part, spinous : the eyes are 

 placed on the same side of the body ; and this side, 

 which is the upper surface, is coloured so as to resemble 

 the ground upon which these fishes lie in wait, among 

 mud, sand, and weeds, to seize their prey : the under 

 surface, from never being exposed to the action of the 

 light, is always colourless, and generally of a fleshy 

 white : the scales are small and well-defined : and the 

 whole of the species are marine. They are, however, 

 very few in number when compared with the Sal- 

 monidce, and present but few variations in their general 

 structure. 



(206.) The Gadidce, or cod-fish, also form but a 

 small family, although with several well-defined "vari- 

 ations of structure. They have the usual shape of 

 ordinary fishes, and are entirely marine. The small 

 scales of the body are covered, and often nearly 

 concealed, by a mucous skin, which also extends over 

 the fins, and gives them a thickened and fleshy cha- 

 racter, not found in the Salmonidce. The head and 

 body is generally but slightly compressed, the eyes- 

 large, and the mouth very wide. The ventral fin in 

 this group, is very small, and generally terminates in a 

 pointed fleshy filament, more or less lengthened ; and 

 three out of the five rays usually found in this fin are 

 sometimes wanting : this character, hitherto overlooked, 

 we shall subsequently find to be of much importance. The 

 Gadidce present considerable variation in the apparent 

 number of their dorsal fins ; in some there are three, in 

 others two, and in a few only one ; but the interval 

 of their divisions are so small, that, perhaps, it would 

 be more correct to consider them as having one long 

 dorsal, variously cleft : the snout is often furnished 

 with small cirri , or round worm- shaped filaments. 



