2 oo CONCHIFERA. 



it is admirably adapted. The animal lengthens the foot into a wedge, which 

 it Jhrusts deep into the sand, and then, turning the end into the shape of a 

 hook, and thus acquiring ahold, it drags itself down, and becomes buried so 

 deeply, that only the projecting ends of the tubes, through which it breathes, 

 are visible. By an opposite process, bending the end of the foot, and pushing 



FIG. 202. TELLINA. 



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 Madras, and a host of others of similar 

 conformation. 



The fifth family of Conchiferous Mollusks has received the 

 name of 



Inclusa (Enclosed], the animals having the margins of the mantle, with 



FIG. 203. THE SANDGAFER. 



the exception of a single opening for the passage of the foot, completely united, 

 so as to form a double tube, the end of which can be protruded to a consider- 

 able distance from the shell, that gapes more or less widely to ^ive it passage. 



