GASTEROPODS 



365 



glutinous secretion which hardens in water, and, being filled with 

 air-bubbles, constitutes a float. On the under side of this are 

 deposited the eggs in rows of little capsules. While attached to 

 this float it is impossible for a Janthina to sink, and hence it is 

 that so many of these creatures are sacrificed in onshore gales of 

 wind. 



<7. frugilis. The shell of this species is so brittle and fragile that it 

 is very clearly not adapted to a life near shore. It is in reality a pelagic 

 species which is occasionally blown ashore during easterly gales along 



FL 



Janthina fragilis : FL, float ; O, ova ; Pr, proboscis ; Ttr, branchiffi ; F, foot. 



the Atlantic coast of the United States. Vast numbers of these pretty 

 creatures are sometimes encountered far out at sea, floating quietly on 

 the surface. When storms drive them upon the beach, they become 

 utterly helpless ; since their foot is not adapted for crawling upon the 

 sand, they soon perish, and their brittle shells are demolished by the 

 surf. In Florida the beaches are sometimes fairly lined with Janthina 

 shells, which make a band of purple along the high-tide mark as far as 

 the eye can reach; then it may be years before they again appear. 

 (Plate LXVIII.) 



FAMILY SCALIDJE 

 GENUS Scala 



The shells of Scala have such a peculiar scheme of decoration 

 that once seen they can never be mistaken. They are generally 

 pure white, with well-rounded whorls, all of which are crossed at 

 even distances by greatly elevated and smooth ribs. Each rib 

 represents a rest-period, when the creature thickened the rim of 

 the shell-aperture. The aperture is generally round, with a con- 

 tinuous lip. The animal has a retractile proboscis and long, 

 slender tentacles with eyes at the outer bases, and is a predaceous, 

 carnivorous creature. Some Asiatic species of this genus, remark- 



