30 American Seashells 



famous workers such as Gunnar Thorson, Marie Lebour and others. The 

 common European Periwinkle {Littorina Httorea) will serve here as an ideal 

 example of the pelagic type of development. The female spawns two to 

 twelve hours after copulation by the male. About 200 single q^^ capsules 

 are shed during the night. During the entire breeding season of six months, 

 the total number of tgg capsules per female is estimated at about 5000, and 

 a half dozen copulations are necessary to ensure fertilization of all the eggs. 

 The helmet-shaped capsules are shed freely and float about in the water. 

 Each contains from one to nine eggs. The free-swimming young, called 

 veligers, hatch on the sixth day and remain afloat for two weeks or more, 

 depending upon temperature conditions, then sink to the bottom and begin 

 an adult snail's life of crawling. They reach maturity on the second or third 

 year and may live for five to ten years. 



In contrast to this mode of spawning, the Left-handed Whelk of Florida 

 {Busycon contrarhmi) lays its horny strings of t'g^g capsules during a rela- 

 tively short period of a few weeks. On the west coast of Florida egg-laying 

 usually takes place in the spring. The female digs down well below the 

 surface of the sand and attaches the first few capsules to a buried rock or 

 broken shell. As the process of extrusion of the t^g capsules continues, the 

 female moves toward the surface until its siphon can protrude into the water 

 to allow easy respiration. As more capsules are made, the string may loop 

 out into the water above the hidden adult. From five to fifteen cases may 

 be formed each day, and a completed two-foot-long string may have nearly 

 a hundred capsules. Within each case there may be two to twenty-five eggs 

 which in a few weeks will develop to quarter-inch-long young. These minia- 

 ture replicas of the adults eat their way out of the case at a special "door" 

 and commence crawling and feeding immediately. The Left-handed Whelk 

 begins spawning at a relatively early age, commonly when no larger than 

 three inches. In such cases the capsules are only a half inch in diameter, 

 while larger females may produce capsules about the size of a half dollar. 



