CLAMS, MUSSELS, AND OYSTERS. 



37 



CHAPTEE yi. 



OLAMS, MUSSELS, AND OYSTEES. 



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

 a lot of bivalves, as the clam, mussel, razor-shell, oyster, seal- 

 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-Watek Bitaltes. 



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 t]ie fresh-water mussels. 



