MOLLUSCS: THE MOLLUSCS 247 



class show a range in size from the little fresh-water 

 Cyclas about I cm. long to the giant clam of the Indian 

 and Pacific islands "which is sometimes 60 cm. (2 feet) 

 in length and 500 pounds in weight." They show also 

 some variety in the form and appearance of the shell, but 

 not anything like the degree of variety shown by the 

 shells of the Gastropods. 



The edible clams are of several different species. The 

 hard-shell clam (Venus mercenaria), or "quohog "as it 

 is often called, is found along the Atlantic coast from 

 Texas to Cape Cod. It is "common on sandy shores, 

 living chiefly on the sandy and muddy plots, just beyond 

 low-water mark. ... It also inhabits estuaries, where it 

 most abounds. It burrows a short distance below the 

 surface, 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. . . . 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 the 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 fcecal 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 siphons are closed and partly withdrawn."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 



