THE ANIMALS AND MAN 



but is frequently found crawling at the surface with the shell 

 partly exposed." The shells of this edible clam are white. 

 The soft-shell clam (My a arenaria), "the clam par excellence, 

 which figures so largely in the celebrated New England clam- 

 bake, is found in all the northern seas of the world. 



FIG. 83. California mussels and barnacles on rocks, exposed at low 

 tide. (Photograph by the author.) 



* 



All along the coasts of the eastern States, every sandy shore, 

 every mud flat, is full of them, and from every village and 

 hamlet the clam-digger goes forth at low tide to dig these 

 esculent bivalves. The clams live in deep burrows in the 

 firm mud or sand, the shells sometimes being a foot or 

 fifteen inches beneath the surface. When the flats are 

 covered with water his clamship extends his long siphons 

 up through trie burrow to the surface of the sand, and 

 through one of these tubes the water and its myriads of 

 animalcules is drawn down into the shell, furnishing the 

 gills with oxygen and the mouth with food, and then the 

 water charged with carbonic acid and frccal refuse is forced 

 out of the other siphon. When the tide ebbs the siphons 

 are closed and partly withdrawn." Ocean clams and 

 mussels have furnished food for man for ages, and along 

 coasts are found here and there great mounds made of heaps 

 of clam-shells which have become covered over with soil 



