40 CLASSIFICATION' OF FISHES. 



division the pectorals are larger than usual, and the 

 ventrals often remarkably developed : in a fourth, these 

 latter fins are quite the reverse ; they are either small, 

 very imperfect, or altogether wanting, while the dorsal is 

 long and often very broad : finally, there is a fifth form 

 where the first dorsal is short and triangular, and the 

 second long and narrow, as in those two well-known 

 genera Trachinus and Ui-anoscopus^ Numerous ex- 

 amples of the prevalence of these forms, following each 

 other in a natural series of affinity, may be traced in 

 the synoptical definitions of the arrangement we have 

 made of this class : and although the preceding remarks 

 are more particularly drawn from the two typical orders, 

 instances are not wanting to show the same tendency 

 in the more incomplete or aberrant orders. 



(42.) We may here explain the terms by which we 

 propose to designate the different forms of the fins, and of 

 their relative situation. The true length of a fin should 

 probably be reckoned from the base to the tip of its 

 rays, while its breadth would be estimated by the -ho- 

 rizontal space it occupied between one extremity of 

 the body and the other ; but this terminology, however 

 abstractedly just, would be in complete opposition to 

 the terms we apply to the figure of the fish itself, and 

 might lead therefore to some perplexity. We may 

 take the eel as an example : we should say that this 

 fish is very long, and justly so ; but although its dorsal 

 fin extends to near its entire length, we must describe 

 this fin, in accordance with the foregoing rule, as very 

 short, because the length of the rays (not the fin itself) 

 is really so ; while, by the same rule, we must term the 

 body very narrow, and, the dorsal fin very broad. To 

 common apprehension, these terms would seem to con- 

 tradict each other: and, in truth, the subject is beset 

 with some difficulty. It seems to us, however, that by 

 looking to the fin itself, instead of its rays, we may 

 get a greater 'Uniformity of terms than by any other 

 rule. Thus, we should describe the dorsal fin of the 

 eel as very long, but very narrow or low ; and that of the 



