CHAMA. 63 



productions, and is sometimes as much as two 

 feet or more in breadth. The oval, or rather lan- 

 ceolate opening in the posterior slope, is probably 

 made use of by the fish to eject a byssus, with 

 which it fastens to rugged substances and resists 

 the action of the waves. 



The very incongruous varieties of external forms, 

 of surface, and of general character, which distin- 

 guish the several species of the 2d section, render 

 it impossible to offer a good example in illustration 

 of the family ; it has not, therefore, been attempted. 

 Although the margins in this division be not all 

 perfectly closed, yet they are comparatively so ; 

 and are obviously separated merely as a passage 

 for nutriment, not for any substance such as a 

 bunch of adhesive filaments. 



