304 Shell Life 



mata ; those which in the adult state have neither 

 shell nor mantle constitute the Gymnosomata. They 

 never come near the shore of their own will, for they 

 are purely pelagic, but many come to land nolens 

 volens in storms and are destroyed in thousands. 

 None of them can be said to be truly British, but 

 the remains of three or four species have been taken 

 in sufficient numbers and with such frequency that 

 they must be included in the British list. 



Lionacina retroversa is one of the shell-bearers. 

 Its body is more or less tinged with purple, and 

 the so-called " wings " of the foot are very large, 

 with a supplementary pair one-third of their size. 

 The shell is extremely thin and fragile, 

 almost transparent and clear, but with a 

 suggestion of yellow when tenanted by 

 the living mollusk ; there is a tiny 

 glassy operculum. It is a common and 

 abundant species, and its empty shell 



Shell of Limaclna i p i • i n 1 



may be round m sand on all our shores 

 where strong currents wash up material from the 

 deeper waters far out. But the living animal has 

 been rarely found in our waters. Forbes found it 

 to the north-west of Skye in 1850; Canon Norman 

 and J. G. Jeffreys took it in Shetland waters in 

 1861 and 1867 ; and M' Andrew caught several about 

 fifteen miles south of Mizen Head, Ireland. Their 

 position in swimming and floating is reversed — the 

 shell below, the foot expanded above. Tlieir so-called 

 flight is a movement straight up through the water 

 by jerks, effected by depressing tlie wings. By keep- 

 ing these organs spread they can remain suspended at 

 the surface or at some distance below it, but on folding 



