SEA MUSSEL MYTILUS EDULIS. 131 



The class Lamellibranchia is the most important of all from the commercial stand- 

 point. It includes the oyster, which furnishes the most valuable fishery of the nation, 

 the receipts from this source alone amounting to one-third the total income derived 

 from all the fisheries of the United States. The flesh of the oyster constitutes a most 

 delicious morsel, and the shells are used in the construction of roads, as a food for 

 poultry, as fertilizer, and as cultch for starting new oyster beds. About 25,000,000 

 bushels of oysters are utilized in the United States annually. Other valuable edible 

 lamellibranchiate species are the clams Mya and Venus, which have made the New 

 land clam-bake famous throughout the land, and the scallops, which are popular in 

 every hotel and restaurant of our northeastern coast. 



The fresh-water mussels of our inland waters furnish pearls of rare value and 

 shells especially adapted for the button industry and for the manufacture of articles of 

 much beauty. So great has been the demand in recent years for the important species 

 that the resources have been greatly depleted. Fortunately, however, the United States 

 Bureau of Fisheries has been able to take up the problem, and, by the application of 

 scientific methods, it is now propagating mussels to provide for the increased demand. 



Not only do the lamellibranchs yield products of commercial value, but in their 

 daily functions they perform a service which has never been estimated in dollars and 

 cents. Their habit of setting up currents of water which are continually filtered through 

 the gill filaments serves to remove the bacteria and other microorganisms along with 

 quantities of floating organic particles which, if left in the water, would lead to stag- 

 nation. They constitute, therefore, one of the great purifying agents of our lakes, 

 ponds, and streams. 



The United States Bureau of the Census reported the value of the mollusk fish- 

 eries of the United States for 1908 as follows: 



Oysters S15, 713,000 



Hard clams I »3 I 7. 000 



Long clams 553, 000 



Scallops 317,000 



Fresh-water mussel shells 392, 000 



Slugs and pearls 300, 000 



Sea mussels 11, 600 



Oyster and other shells 20, 000 



Squid 43, 000 



Cockles, winkles, conchs 35, 000 



Total 18, 701, 600 



ANATOMY AND PHYSIOLOGY OF THE SEA Ml/SSEL. 



THE SHELL. 



DESCRIPTION. 



• 



The sea mussel has a general form which may be described as triangular ovate. 

 Anteriorly, in the hinge region, the shell presents its greatest breadth; posteriorly, it 

 becomes narrower and flattened. The posterior edge of the shell is nearly semicircular 

 in outline; in the dorsal region it forms almost a straight line up to the beginning of the 

 hinge, where it bends obliquely downward at an angle of about 45 to the umbo, which 

 is located at the tip of the shell. From the sharp point of the umbo the ventral edge of 



