MOLLUSCS. 325 



The Ianthinid^ are remarkable for the beautiful purple color of their thin shells. 

 They are pelagic, oceanic snails, which lead a predaceous life. At times on the high seas 

 the navigator encounters vast numbers of them, forming immense schools, and feeding 

 upon the other forms of life ; medusae, Crustacea, etc., with which they are surrounded. 

 The animal has a large head furnished with an extensible proboscis. The eyes are 

 minute and situated on the extremities of the ocular peduncles, while the foot is small 

 and divided. The shells are thin and delicate, the whorls of the spiral being few in 

 number. At the base they are of a deep violet color, but the apex is nearly or entirely 

 white. 



One of the most interesting features connected with these shells is the enormous 

 float which they form to support the eggs. The foot secretes a glutinous secretion 

 which hardens to a slight extent when brought in contact with the water. During the 

 reproductive season the formation of this egg float is continuous, and, as it is formed, 

 eggs are fastened to its lower surface. From this mode of formation, that part of the 

 float farthest from the animal contains the most advanced eggs ; and, in fact, the eggs 

 in this portion may have hatched and the embryos have begun their free life ere those 



Fig. 404. — lanthinaj purple shell, with the float supporting the eggs. 



nearest the body have passed through the earlier stages of development. Although 

 the parent usually carries the float attached to the body, still it has apparently the 

 power to east it off at will, while the action of stoi-ms usually separates the mother 

 from the egg. When thus cast adrift, the float still sustains the eggs, and they pursue 

 their development as usual. Each egg is fastened to the float by a short peduncle, 

 while the float itself is composed of numerous little bubbles, thus securing great 

 buoyant powers. 



The lanthince do not appear to have the power of sinking in the water unless 'the 

 float is detached, and so at the time of storms they are frequently cast upon the shores 

 in large numbers. At such times they are utterly helpless and make no attempts to 

 crawl. They, however, frequently adhere to each other by means of the foot, and, 

 when handled, secrete a violet-colored fluid. 



lanthina, the most prominent genus, contains about ten, species, one of which (1. 

 fragilis) is occasionally thrown up on the southern New England coasts by severe 

 sou,theast storms. It is not properly a member of the American fauna, but like the 

 rest of the genus is an inhabitant of the high seas. The only other living genus of 

 the family {Recluzia) is covered with a brownish epidermis. Like lanthina, it forms 

 a float. 



The SoLAEiD^ embraces a group of molluscs which, from the shape of the shell, 

 was formerly included in the Trochidse. The shell is orbicular and forms a more or 



