8o IN LOWER FLORIDA WILDS 



for this reason, is rarely found alive. But here 

 the strong currents, no doubt, destroy the burrows 

 and wash out the mollusk. Its beautiful detached 

 valves, sometimes eight inches long, often lie on 

 the beach in ricks. They are thin, peculiarly cor- 

 rugated, and shaped somewhat like the wings of 

 the angels in old pictures; this and their pure 

 white color have suggested the name. 



The Pholads, of which this species is fairly 

 typical, are a large and diversified family, all of 

 which are borers. Some of them, like the present 

 species, dig only in sand or mud; others excavate 

 their tunnels in wood or soft rock, and some bore 

 out their nests in hard granite. For a long time 

 the manner of their working was a mystery and by 

 some it was believed that the boring was done by 

 the edges of the rough, corrugated shells, but it is 

 now known that this is not true. There is a set of 

 strong muscles attached to winglike processes out- 

 side and at the back of the shell. These muscles 

 can be powerfully contracted by the animal so that 

 the two valves or shells are drawn wide open and 

 their rough surfaces held very firmly against the 

 walls of the burrow. With the shell thus held fast 

 the animal turns and twists its large foot, which 



