FILE-FISHES. 



685 



smaller, and frequently beautifully and symmetrically marked. 

 Both jaws are armed with eight strong incisor-hke and 



Fig. 310. — Balistes vidua. 



obliquely truncated teeth, by which these fishes are enabled 

 to break off pieces of corals on which they feed, or to chisel 

 a hole into the hard shell of Mollusca, in order to extract the 

 soft parts. They destroy an immense number of Mollusks, 

 thus becoming most injurious to the pearl-fisheries. The first 

 of their three dorsal spines is very strong, roughened in front 

 like a file, and hollowed out behind to receive the second 

 much smaller spine, which, besides, has a projection in front, 

 at its base, fitting into a notch of the first. Thus these two 

 spines can only be raised or depressed simultaneously, and 

 the first cannot be forced down, unless the second has been 

 previously depressed. The latter has been compared to a 

 trigger, hence a second name, " Trigger-fish," has been given 

 to these fishes. Some species are armed with a series of short 

 spines or tubercles on each side of the tail. Two species {B. 

 maculatus and B. capriscus), common in the Atlantic, some- 

 times wander to the British coasts. 



The MonacantJms are similarly distributed as the Balistes, 

 and still more abundant, some fifty species being known. 

 Their dentition is very similar, but they possess one dorsal 

 spine only, and their rough scales are so small as to give a 



