CLAMS, MUSSELS, AND OYSTERS. 



41 



ex. ^n. 



B -A f 



FIG. 42. COMMON CLAM. A. showing Siphons partly extended; in., Incurrent Orifice; ex., 

 Excurrent Orifice ; /, Foot ; ?, thickened border of the Mantle projecting beyond the 

 Edge of the Shell; B, Siphons, greatly extended. (The shell is not drawn, as there was 

 no room for it on the page.) The excurrent and incurrent orifices are more open than in A. 



