MOLLUSCA 



53 



shell is not fit for food but it cannot contaminate those that are still 

 closed. 



The custom of " floating" oysters has been considerably discussed. 

 By a "floated" oyster is meant one that has been brought into water 

 of less salinity than that in which it grew, until it has absorbed this 

 fresh water and thereby become swollen or bloated. This custom, when 

 the fresh water is contaminated by sewage, as it often is near cities, 



FIG. 35. Long-neck clam, My a, with byssus, b, attached to sand grains, sg. 

 J. L. Kellogg, Shellfish Industries.) 



(After 



was a serious source of contamination and was justly condemned; but if 

 the water be pure the floating merely makes the oysters bulkier (by as 

 much as 20 per cent., at times), and thereby diminishes their food value, 

 when bought by the quart or gallon. For this reason the pure food 

 laws require "floated" oysters to be so labeled. The floating also 

 diminishes the salty taste of the oysters, which makes them more agree- 

 able to some palates. 



Soft or long neck dam, Mya arenaria, Fig. 35. This is the clam 

 of New England, famous in clam chowders and clam bakes. It is 



