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. 
