165 
BONY FISHES. 
The large family of bony fishes, or Acanthopterygians, is 
readily distinguished from the Plagiostomes, and from a third 
that will follow, by marks which are easily recognised; 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 difi'er 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. 
