24 



R E .M ARKS. 



It seems necessary to mention, that in the descrip- 

 tion of the bivalves, I adopt the arrangement insti- 

 tuted by Broderip and Sowerby, and term the dis- 

 tance from anterior to posterior extremity, the 

 length 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 aii- 

 rhors. I make no innovations, but merely adopt 

 sncli a mode of description used by others as seems 

 most natural and intellijriblc. 



