MOLLUSKS 



135 



and is fastened to the rock or other body upon which the jingle 

 shell is growing. This stalk of attachment is in reality the byssiis, 

 and when first formed it is flexible as are the attaching threads of 

 many other clams and mussels. 



The jingle shell is foimd from the West Indies to Cape Cod, 

 and is very abundant in Long Island Sound. It is, however, rare 

 north of Massachusetts Bay, 

 although it has been found as "^ 

 far north as Cape Sable. It is a 

 shallow water form, not living 

 at a depth greater than 70 feet. 



The dead shells are of 

 considerable commercial im- 

 portance, for they are used by 

 the oystermen to be strewn 

 over tlie beds in order to give 

 the little oyster a good surface 

 upon which to set. The shell 

 is well figured in Verrill and 

 Smith's "Invertebrates of 

 Vineyard Sound," p. 17 (.311), 

 Plate XXII, Figs. 241, 242, under the name of .\iiomia ijlabra. 



The Pearl Oyster, ( Meleagrina marcjaritifera). This species and 

 several closely related varieties furnish the most valuable mother of 

 pearl and precious pearls known. The pearl oysters are especially 

 abundant in the Indian Ocean and tropical Pacific but they are also 

 found in the Gulf of California, the Red Sea, and sparingly in the 

 West Indies. The fisheries of the Persian G-ulf are worth $2,000,000 

 annually and those of Ceylon are almost as valuable. About 15,- 

 000 tons of pearl shells are used by the world each year, the value 

 of which ranges from about $900 to $250 per ton. The pearl 

 oyster is a large, flat l)ivalve, with a long, straight hinge, and quite 

 regularly curved contour to the shell, and is about ten inches Ijroad. 

 On the outside the shell is dark-olive often mottled with irregularly 

 crescent-shaped yellowish spots, or streaked witli l)roken yellowish 

 lines radiating from the apex. The outer skin of the shell is rough 

 and flakes off into long, ragged, scale-like projections, especially near 

 tlie outer edges. Inside one finds the lieautiful nacre of the shell 



Fig. g7: 



.IIXfiLE SHELL UPON A ROCK. 

 Long Isl;lnd Soiiud. 



