MOLLUSKS 127 



and muscular and its end flattened to serve as a pushing organ. 

 The clam burrows onl}- a short distance beneath the sand and occa- 

 sionally comes to the surface where it literally skips along by means 

 of its powerful foot, aided by the flapping motion of its valves. In 

 common with all other clams it feeds upon minute organisms both 

 vegetable and animal. 



The Swimming Clam, (Solenomya velum. Fig. 86 J, ranges from 

 North Carolina to Nova Scotia, where it burrows into sandy or 

 muddy beaches immediately be- 

 low tide level. In common with 

 tlie razor clam, and sand-bar 

 clam, it prefers pure ocean water. 

 It is not over three-quarters f»f 

 an inch in length, and the sliell 

 is thin and flexible with a ricli 

 brown surface varied by yellow 

 lines radiating from the hinge. ^^^- »(>-■ swimming clam, cape 



mi c c 1 • 1 T Ann, Mass. 



The foot of this clam can be ex- 

 panded into an umbrella shape at its apex. When the foot is 

 expanded and driven suddenly outward, the clam swims backward, 

 but when the foot is suddenly withdrawn it swims forward. In 



this manner the clam is enabled to swim for 

 a considerable distance through the water with- 

 out touching the bottom. 



The Bloody Clam, (Argina pexata, Fig. 



87 J, is common under stones or within gravelly 



beaches, below^ low-tide level, from Florida to 



Cape Cod. It attaches itself to stones by 



means of a byssus thread which is secreted by 



— -^ a gland in the foot. The shell is oblong, about 



F!£:. sy/ BLOODY one and one-quarter inches wide, and covered 



with a rough, brown skin. There are about 32 



ridges that radiate outward from the beak of the shell. The gills 



and circulatory fluid of the clam are red. Hence the popular name 



of "bloody clam." 



The Ship-Worm, or Teredo, (Fig. 88), is not a worm but is 

 closely related to the clams. Its peculiar elongate form and worm- 

 like appearance are due to its habit of burrowing into any sort 



