CLAMS, MUSSELS, AND OYSTERS. 



37 



CHAPTER YI. 



CLAMS, MUSSELS, AND OYSTERS. 



36. CLASSES having access to salt-water may now collect 

 some bivalves, as the clam, mussel, razor-shell, oyster, scal- 

 lop, and whatever species they can find belonging to this 

 group. A much greater variety of forms will be found in 

 salt-water than in fresh-water. 



Among some of the common species met with will be 

 the following : 



FIG. 40. SALT-WATER BIVALVES. 



In these the pupil may trace out the muscular impres- 

 sions within the shell, and make out their relations to the 

 impressions already described in the fresh-water mussels. 



