16.5 



BONY FISHES. 



The large family of bony fishes, or Acanthopterygians, is 

 readily distinguished from the Plagioslomes, and from a third 

 that will follow, by marks which are easily recognised j and 

 which also are closely associated with the instincts and modes of 

 life of the several subordinate tribes of which this class is 

 composed. The visible prevailing characters are, that the jaws 

 are nearly equal, and at the extremity of the head. Every 

 departure from this particular will appear only relative. In 

 their mode of formation as well as generally in shape, their 

 teeth differ from those of the Sharks, in having their origin 

 in a membrane which lies along the border of the jaws, and 

 they rise directly from this portion of their gum, with their 

 points upward, into the place where they are to remain, sup- 

 plying the place of such as have already performed their 

 duty, and, by losing their attachment, are about to be shed. 

 There is, therefore, a perpetual succession, but it is of indi- 

 viduals and not of ranks. They are attached to, but do not 

 penetrate into the jaws; and the formative membrane does not 

 perish, as in Sharks, with the teeth it had formed. The 

 nostrils are usually double, and of small size, placed above 

 the line of the snout, and before the eyes. The gill openings 

 are single on each side, with often a wide aperture,^ and 

 usually also with a gill membrane, furnished with bones. The 

 body is. for the most part, covered with scales; the fins 

 usually stand on joints, often with firm spines, and the mem- 

 brane is usually to be easily distinguished from the rays, even 

 when the structure is less firm. The tail partakes of the 

 nature of the other fins; the vertebra ending in a separate 

 plate, perhaps divided into branches at its root; and to it the 

 caudal rays are attached. 



VOL I. 2 B 



