The Slipper Shells. Cup-and-saucer Limpets 



parties. There is never any scarcity of dishes ; the tide is always 

 bringing in new ones. 



Grown-up people, too, find a use for the empty shells. Fisher- 

 men at Greenport, Long Island, dredge up the accumulation of 

 dead shells and sell them to oyster growers for "stool." This 

 means that they are scattered over the rocky floor of new 

 beds for the embryo oysters to settle upon. "Quarter-decks" is 

 the trade name they go by. They are taken with the "jingle 

 shells," which frequent the same banks, and are also excellent as 

 oyster stool. In 1887 Greenport alone sold 130,000 bushels 

 of the two shells to the oyster growers for 15,200, an average 

 price of four cents per bushel. 



English oyster beds are in some places replenished with 

 "seed" from American growers. With these young oysters 

 C. fornicata has been introduced. Conditions are favourable to 

 growth, and the "crow oyster," as it is called, has become a nuis- 

 ance. The edible oyster, when overloaded with slippers, often 

 three to six deep, is stunted and unsightly. The parasites rob 

 the oysters of their food, and choke them besides. There seems 

 to be no way of getting the better of the invader. 



This species is the largest of its genus; the shells are from 

 one to two inches long. The spiral apex is drawn down to one 

 side of the posterior end of the shell. From it indistinct lines 

 of pinkish brown, often broken into dots or broadened into 

 streaks, paint the almost smooth surface. The polished interior 

 is mottled with brown and violet in large patches. The par- 

 tition is white and thin. 



The height of the shell arch is largely dependent upon the 

 life of the mollusk. Some individuals are free, and have very 

 concave shells, others affix themselves to stones, or to the shells 

 of oysters and various other mollusks. These are modified in 

 form by the surface to which they adhere. On a scallop shell 

 the Crepidula will be ribbeid. Sometimes slippers are found 

 piled one upon another in tiers of six or more. This is especially 

 common in northern waters. They feed upon seaweeds for the 

 most part, but have been known to eat other mollusks. 



It is known that some of these mollusks move, and perma- 

 nently change their positions. A certain specimen may spend 

 a part of its life on a ribbed shell like an Area or a Pecten, then 

 move to a smooth shell or stone. The growth of the shell will 



149 



