MOLLUSKS 123 
constant current providing fresh water to breathe, and also drawing 
into the shell the food of the oyster. The organisms serving as 
food are caught in the slime covering the gills, and are swept into 
the open mouth by the action of the cilia. Oysters are capable of 
detecting sound, for they close immediately when a loud noise is 
produced. 
The Surf Clam, (Mactra solidissima, Fig. S1). This is also 
called the hen-clam. It extends from the Gulf of Mexico to Lab- 
rador, and is 
found on sandy 
beaches from low 
water to a depth 
of about sixty 
feet. The shell 
is covered with a 
horny, light- 
brown skin, and 
is not deeply fur- 
rowed by lines of 
growth. It grows 
to be fully six 
inches long and 
four wide The Fig. 81; SURF CLAM. From life. Young and old. 
: = Annisquam, Mass. 
siphon is_ short ; 
and thick, while the foot is large, stout and muscular, and enables 

the clam to dig rapidly into the sand. It does not construct a deep 
burrow, however, but lives quite close to the surface, and is on this 
account often cast ashore by storms. Its flesh is tough, and not 
highly esteemed as food. 
The Soft-Shell Clam, ( Mya arenaria, Fig. 82). This is often 
called the ‘long clam” or ‘“‘nanninose.” It is found in sandy or 
muddy shores from the Carolinas to the Arctic, and also on the 
Northern coasts of Europe. It is common in the sheltered banks 
of bays and estuaries between tide limits, where it burrows in the 
ground by means of its muscular foot, having its long, extensible 
siphon pointing upward. When the tide is high the siphon is 
extended so as to reach to the opening of the burrow, but it retracts 
