THE CLAM AND OTHER BIVALVES 165 



If a young clam escapes the danger of being carried out 

 to sea during its pelagic life, it is safe for a while when, on 

 sinking to the bottom, it anchors to some fixed or heavy ob- 

 ject with its byssus-thread. There it encounters dangers from 

 food-hunting fish. Still more dangerous are the storms that 

 carry waves of water far up the beach and leave to destruction 

 many kinds of animals that happen to be borne along. At 

 the same time countless young of the clams that escape being 

 carried out must be smothered by the shifting sand and mud. 



As the adult stage approaches the dangers of existence 

 become less and less, until man himself interferes with the 

 natural balance of chances in the clam's life. In certain 

 parts of the Atlantic coast, especially in the vicinity of large 

 cities, the species is fast being exterminated. Although the 

 clam is not as highly esteemed as an article of human food 

 as its relative the oyster, it is nevertheless of great value. 

 Officers of the Bureau of Fisheries have considered the mat- 

 ter of restricting the digging of clams, and also various means 

 of tiding the young over the danger-points in their lives. 



THE AMERICAN OYSTER 



Habitat and Distribution. The American oyster (Os'trea 

 virginia'na, Fig. 85) is found in shallow to deep water along 

 the Atlantic coast from the Gulf of Mexico to Massachu- 

 setts Bay. As the artist has shown in the picture, the animal 

 lies attached to the bottom, frequently to another oyster-shell. 

 Although many oysters may live thus fastened to each other, 

 there is no organic connection between them. They some- 

 times form clumps so large and heavy that the basal ones 

 sink into the mud and die. The valves of the living ones 

 extend outward at any angle. When oysters are not crowded 

 iri the " bed," the usual method of living is the one shown 

 in the illustration. There the valves extend horizontally, 



