Pelecypoda. 



121 



burrow. The internal structure is essentially the same as in 

 the fresh-water clam. To accommodate the long siphon 

 tube when it is retracted, there is a deep indentation of the 

 mantle line in the posterior region. The shell of Mya can- 

 not be snugly closed, there being a gap both anteriorly and 

 posteriorly. Probably this may be accounted for by the 

 more protected position and the need of having the siphon 



FIG. 75. HARD CLAM ; ROUND CLAM ; QUAHOG. 



With foot, siphons, and edge of mantle extended. 



tube extended most of the time. The siphon tube, with its 

 black tip, is commonly called the " head," but this clam is 

 as headless as its fresh-water relative. 



The Hard Clam. The hard clam, or quahog, is also an 

 important sea-coast food, especially where the soft clam 

 is not obtainable. It is oval, with a thick shell. It bur- 

 rows but a short distance, hence the siphons are not long, 

 and the two tubes are partly separated. The foot is well 

 developed, and the clam crawls more or less like the fresh- 



