34 CLASSIFICATION OF FISHES. 



of equal length, the central ones not exceeding the 

 others,, while the outermost ones are rounded at their 

 angles only. Many of Cuvier's genus Serranus have 

 this fin, also nearly all the sticklebacks (Gasterosteus), 

 Sciana aquila (Cuv. pi. 100.), Blepsias (lb. 90«)> l^ra- 

 noscopus, Priacanthus, Hemitripterm, &c. — 5. Trun- 

 cate : when the extremity of the fin appears to be 

 abruptly cut off, so that the external rays are just as 

 long as those in the middle, and the angles are not 

 rounded, as in the last. Zeus and Trachinus may be 

 cited as the most familiar examples of this form, which 

 is only distinguished from the next by the marginal ex- 

 tremity of the fin being in no degree concave or cres- 

 cent-shaped, or, in other words, not having the central 

 rays shorter than the external : it must be observed, 

 however, that fins of this description can only be de- 

 tected when extended ; for when closed, the margin 

 generally has the appearance of being slightly concave. 

 (36.) Forked caudal fins are as much, and even 

 more, varied than the last. The incipient develop- 

 ment of this structure is seen in such as have the mar- 

 ginal extremity slightly concave, as in the majority of 

 the Triglidce. or gurnards, the angles being pointed, and 

 the interval between them slightly hollowed out, so that 

 the central rays are shorter than the external ones. 

 Trachinus radiatus, according to Cuvier (pi. 6l.), has 

 a concave fin, although in the common species of the 

 Mediterranean it is completely truncate. This is a very 

 prevalent form, and several examples occur in the sub- 

 family of the Scicenince, as Leiostomus, some Corvince, 

 &c. — The lunate shape is on the same principle 

 as the last, but the concavity of the margin is much 

 deeper, and the two extremities are prolonged, often 

 (as in Naseus, some of the sub-genera of Acanthurus, 

 &c.) to an excessive length, in the shape of filaments. 

 Forked caudals, properly so called, are of two kinds : 

 in one, the divisions are equal {fig. 4. d) ; in the other, 

 unequal (c). The most typical of the first form, as be- 

 fore intimated, is universal among the Scomberidce, or 



