120 MADRAS FISHERIES BULLETIN VOL. XIV, 



where it assumes the form and function of a plough to push the 

 sand away on both sides as it burrows. In these animals the shell 

 is ear-shaped with a very wide aperture; the operculum is minute 

 and of no protective value to its owner- 



The lovely VIOLET SNAILS {laiithinidac) are purely pelagic ; 

 they are found floating at the mercy of the currents in all warm seas ; 

 particularly common in the Indian Ocean, their beautiful violet 

 tinted papery shells are common objects along the shore after long 

 continued onshore winds. Often they are cast ashore alive and if 

 we put them in a bowl of water we see how cleverly they have 

 overcome the difficulty of keeping afloat. Under natural condi- 

 tions, they float head up with the spire of the shell downwards. 

 The foot is small and attached to it is a long frothy-looking raft, 

 composed of bubbles entangled in a transparent secretion of the 

 foot that dries into a delicate tough membrane. They are gregari- 

 ous and float about in shoals, feeding upon oceanic jellyfishes 



Fig. 13. Life appearance of lanthina, showing the float and the egg-capsules 

 attached beneath. (After Owen ; modified.) 



(Siplionophores), usually tinted violet like lanthina itself. Some 

 species attach their egg capsules to the under side of the float ; 

 others bring forth their young alive. 



Strangely enough in animals that are free-swimming, the eyes 

 are absent. Neither have they any operculum. Several species 

 are found in Indian seas. 



The Cowries {Cyt^racidac) arc amongst the best known of Indian 

 shells; the beauty and variety of their splendidly polished shells 

 render them conspicuous and valued. The adult shell diff"ers in 

 form from any other ; to understand its structure one must examine 

 the stages by which it changes from the immature condition to the 



