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 ScomberidcBy Zeidcs^ &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 SparincB, 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 that 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 



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