144 MADRAS FISHERIES BULLETIN VOL. XIV, 



whereof the anterior pair is the smaller. Each fin is a thin wide 

 lobe with frilled edges, attached to the body by a muscular stalk. 

 When alarmed or disturbed, the animal seeks to escape by throw- 

 ing off its fins ; when cast off, these exhibit slight movement for 

 some time afterwards. With the help of the mobile "tail "and 

 these paired " fins," Lobiger is enabled to swim with ease. The 

 oval shell, slightly convoluted, is transparent and very delicate ; 

 its convex surface is freely exposed on the middle of the back 

 between the fins ; there is no need as in Bulla and Philine to 

 protect it from sand attrition, for Lobiger pursues a free life in the 

 water, never attempting to burrow. The colour of our Indian 

 species is normally a brilliant green, harmonizing with the colour 

 of the sea-grass of the shallows where it abounds. Sometimes 

 minute dark specks are scattered through the green. The ground 

 colour of the fins is green likewise, bordered with a band of coral 

 red speckled with black dots. Lobiger appears to have some 

 power of colour adaptation, for when placed in a white vessel it 

 becomes yellow, the bright red border to the fins disappearing. 

 In Great Britain the place of Lobiger is taken by the little 

 nudibranch Elysia viridis. This though belonging to a group 

 altogether different has almost identical habits and a related 

 scheme of colouring. 



Here are now placed the shell-bearing Pteropods, " Butterflies 

 of the sea " as they are often called. They spend their whole life 

 in the open sea, often occurring in such vast swarms as to discolour 

 the water for miles; they form the principal food of the Baleen 

 Whale. Their shells are either tubular {Crescis) or broad and 

 pocket shaped {Cavolina); the former (Crescis) are common in the 

 minute floating life of our waters (plankton) but so small, pellucid, 

 and needle-like that only under the microscope can it be re- 

 cognized ; the shell of Cavolina is sufficiently stout to be recognized 

 when thrown ashore after storms, usually in company with lanthina 

 and violet-coloured siphonophore jellyfishes. 



The Pteropods differ from other molluscs in the transformation 

 of the foot into a pair of great wing-like swimming fins, arranged 

 one on either side of the mouth, the head as a distinct organ 

 having virtually disappeared. 



The Sea-HaRES (Aplysiidae), so named from a fancied re- 

 semblance to a crouching hare, are heavily built grotesque creatures, 



