CAUDAL FIN. 



35 



mackerel, where the middle of the fin is cleft to its 

 base, or very nearly so ; and each division is falcate, as 

 in the tunnies, or somewhat lanceolate, as in the common 

 mackerel. This form, so prevalent among the genera of 

 the Microleptes (or that tribe which includes the whole 

 of the Scomberidce, Zeidce, &c), hardly exists in the 

 pre-eminently typical tribe of Macroleptes. These latter 

 fishes, on the contrary, have a simply forked caudal ; 

 that is, the lobes are not attenuated, and the central rays 

 are nearly equal to half the length of the external ones. 

 This structure is the most general in fork-tailed fishes, 

 and is generally constant in natural groups, of which 

 the Sparince, the true perches, and several others, afford 

 ample proofs. The most extraordinary development of 

 a simply forked tail, yet discovered, is to be found in 

 the Macropodus venustus (Cuv. pi. 197.):, where the 

 length of this fin is nearly equal to tha*t of the body : 

 and this is the more remarkable, since, in no other genera 

 of its own circle, is the caudal of this form ; a clear 

 indication that it is the rasorial sub-genus. Sometimes, 

 as in Nomeus and Hoplostethus, the caudal, although 

 deeply cleft, has the two divisions rounded ; but this 

 form is very uncommon. — Unequally forked, is when 



one of the divisions of 

 the fin is larger than 

 the other : our English 

 sand-lance (Ammody- 

 tes) shows this very 

 well (Jig. 4. a) ; and it 

 is likewise found in all 

 the flying fish (6), and 

 the greatest part of the 

 sharks and sturgeons. 

 The caudal fins, how- 

 ever, of these latter 

 families are altogether 

 peculiar : the rays are 

 by no means symmetri- 

 cal, so that the upper 

 d 2 



