266 CONCHIFERA. 



FlG. 202. TELLINA. 



The Common Cockle (Cardium), met with upon 

 sandy shores in great abundance, where, under the 

 name of "red noses," they constitute an important 

 article of food. In the Cockles " the foot " is an 

 organ of considerable size, assuming all sorts of 

 shapes. Sometimes it is used for burrowing, for 

 which it is admirably adapted. The animal lengthens 

 the foot into a wedge, which it thrusts deep into the 

 sand, and then, turning the end into the shape of a 

 hook, and thus acquiring a hold, it drags itself down, 

 and becomes buried so deeply, that only the pro- 

 jecting ends of the tubes, through which it breathes, 

 are visible. By an opposite process, bending the end 

 of the foot, and pushing against the sand, at the 

 bottom of its hole, the shell is again extruded. 

 At the bottom of the water the cockle can also move 

 with considerable speed, by pushing with its foot 

 against the ground as a ferryman poles his boat 

 across a river. Nor is this all ; for by stiffly bending 

 the same wonderful organ, and letting it go by a 

 sudden spring-like extension, some species can bound 

 into the air and jump about with considerable 

 activity. To this group belong the beautiful Venus 

 shells (Fig. 195), the Mactrte, and a host of others 

 of similar conformation. 



The fifth family of Conchiferous Mollusks has 

 received the name of 



