THE BALISTIN^j OR FILE-FISH. IQS 



able, in the synopsis_, to determine many of the subor- 

 dinate forms. 



(170.) The BalistincB, or file-fish _, are not so 

 grotesque in their general form as the diodons and 

 tetraodons, and are much more beautiful fish : the 

 colours are generally rich and vivid_, and the body is 

 not armed with spines (-S. erytliropteruSj fig, 27.). 



ViV^ 



The greatest number are confined to the still waters of 

 tropical seas, and principally those of India and Ame- 

 rica. A very singular circumstance connected with this 

 species has given rise to the name now applied to the 

 whole group. The typical Batistes have two dorsal fins, 

 one of which is fronted with a strong bony spine. 

 Salviani was the first to discover that the bones or rays 

 of this fin are so contrived as to act in concert, with 

 considerable force, in suddenly elevating the fin at 

 the pleasure of the animal : though the foremost or 

 largest be pressed ever so hard, it will not stir ; but if 

 the last or least ray of all be pressed but very slightly, 

 the other two immediatelv fall down with it, as a cross- 

 bow is let off by puUing down the trigger. For this 

 reason, the fish is called at Rome Pesce halestra. These 

 fish are provided with true teeth, of which eight are 

 in each jaw. There are no true ventral fins ; but, in 

 most, the bone of the pelvis is prolonged beyond the 

 skin^ and is even furnished with bony rays connected 

 by a membrane, so as to constitute, in effect^ a true 

 ventral fin. 



(171.) We arrange the Balistince under five prin- 



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