138 gangetic fishes. Order V. 



have moveable gill-covers, leaving a large opening on each 

 side. 



In many species, there are one or more bones on the pa- 

 late adjacent to the jaw, and, like this, covered with numerous 

 crowded teeth. And the same is the case with four bones, 

 two above and two below, which many species have at the en- 

 trance into the throat. In a few species, there are either no 

 teeth, even in the jaws, or these organs are extremely minute. 



Although the surface of these fishes has always an uncom- 

 mon number of pores for the secretion of slime, and although 

 they are destitute of scales properly so called, some of them 

 have their sides more or less cased in bony plates ; but, as 

 none of these are among the fishes here described, I shall not 

 dwell any farther on this subject. Many species, however, 

 have no skin on considerable portions of the bony plate, which 

 covers the head, and sends processes along the shoulders and 

 fore part of the back ; nor on a bone, which is placed before 

 the first fin of the back ; nor on a bone analogous to our sca- 

 pulas or shoulder-blades, which extends along the side above 

 the pectoral fin ; nor, finally, on the bone of the breast or 

 sternum. All of these bones, instead of being concealed un- 

 der the skin, have no covering but a thin cuticle, through 

 which they are distinctly visible, and they are usually marked 

 by various elevated ridges, and numerous waved lines inter- 

 secting each other in different directions, or disposed as if ra- 

 diating from different centres. 



Under the lower jaw, and before the os hyoides on the throat, 

 many of these fishes have a transverse slit, resembling some- 

 what a second mouth. It usually forms an angle or curve, 

 with the two extremities turned backward. The slit pene- 

 trates from a tenth to a half inch in depth, in proportion to 

 the size of the fish ; but is lined by a smooth cuticle, nor has 



