CLAMS, MUSSELS, AND OYSTERS. 



43 



42. Fig. 44 represents an animal which is often thrown 

 up on beaches along the coasts, after a storm, and whose shells 

 are very common in the debris thrown up by the waves. 



FIG. 43. A MUSSEL ATTACHED TO A STONE BY ITS BYSSTJS. f, Foot. 



These shells are very thin and delicate, and the valves are 

 strengthened by a thickened rib which runs from the umbone 

 toward the lower margin of the valve within. 



In this species the siphons are united, the mantle projects 

 beyond the edge of the valves, and the foot is flattened in 

 front. 



FIG. 44. I, Ligament; /, Foot; m, Mantle; , Siphons; ecc., Excurrent Orifice; in., Incurrent 



Orifice. 



Fig. 45 represents another animal which is often abun- 

 dant on the sea-beach. In this species the siphonal tubes are 



