CLASS ACEPHALA. 



39 



movement resulting. The byssus is also of use in at- 

 taching the animal to a 

 support. 



The Fresh-ivater Clam, 



FIG. 55. 



FIG. 54, 



I 



mo " 



p 



an \- 



U' '/u o compla na'tus. 

 Fresh-water Bivalve, as it moves through 

 the sand. F, Foot. The arrows indicate 

 the currents of water entering and leav- 

 ing the siphons. 



closely allied to the Mus- 

 sel, is found in all our lakes, 

 ponds, and rivers. This 

 animal, by means of its 

 elongated foot, plows its 

 way through the mud in 

 shallow water. The young 

 have peculiar hooks on the 

 edges of their valves, by 

 means of which they at- 

 tach themselves to the fins 

 and gills of fishes, where 

 they remain for some little 

 time. 



The Salt-water Clam 

 has the siphons united and greatly elongated, enabling 



My' a arena'ria. Common Clam, with left 

 valve and portion of mantle removed, showing 

 the more general anatomical peculiarities, i, Ar- 

 row showing course taken by water as it enters 

 the siphon (s) and bathes the gills, g and y'. 

 Food is directed to the mouth, mo, l>y the palps, 

 p, the water finally leaving the animal through 

 the excurrent opening, e. w. Mantle, with an 

 opening at o, for the foot,/, to protrude. The 

 fleshy body is seen at b. the ligament at /, and 

 the anterior and posterior adductor muscles at 

 aa, and pa. 



