24 
REMARKS. 
Ir seems necessary to mention, that in the descrip- 
tion of the bivalves, I adopt the arrangement insti- 
tuted by BropEerie and Sowersy, and term the dis- 
tance from anterior to posterior extremity, the 
Jength of the shell; the height or elevation is from 
beaks to base. This nearly corresponds with the 
natural position of the shell, when the animal is tra- 
velling in the bed of a stream. The terms compress- 
ed, ventricose or inflated, are probably more descrip- 
tive than broad, narrow, &c. and are therefore used 
in preference, according to the practice of most au- 
thors. I make no innovations, but merely adopt 
such a mode of description used by others as seems 
most natural and intelligible. 
