106 THE MOLLUSCA 



chiefs of the Friendly Islands. Only one specimen (Cyprcea europcea) 

 is found on the British coast. It is a pretty little ridged shell, 

 banded alternately with white and purple or white and flesh 

 colour, and is often further adorned with three dark brown spots. 



The Umbrella-Shell (Umbrella mediterranea), the Sea-hare 

 (Aplysia), and the Sea-lemon (Doris) are typical examples of the 

 third order of Gastropods ; to which also belong the Sea-bubbles 

 (Bullidc?) that flit about in shallow pools on muddy shores, and 

 the Sea-butterflies (Pteropoda) that swim freely in the open sea 

 by means of a curious pair of side fins developed from the neck 

 or mouth. As the little molluscs swim about, these fins flutter 

 like butterflies' wings, and from this they have gained their 

 popular name. 



The quaint Umbrella-Shell is somewhat slug-like in appear- 

 ance, and bears upon its back a small, round, flat shell which has 

 a striking resemblance to a miniature Chinese umbrella, and is 

 quite inadequate as a protective covering to the little animal, 

 though it acts as a shield to its delicate breathing organs, which 

 are situated beneath it. 



The Sea-hare, or Sea-slug, has gained its first popular name 

 from the upper pair of tentacles, which stand erect Upon its head 

 like the ears of a hare. This mollusc bears upon its back a thin, 

 curved, horny shell, but it is very small and almost hidden by 

 the folds of the mantle. The Sea-hare is found in most parts of 

 the world, frequenting rock pools down by low-water mark, and 

 in the shallow waters off the coast. When disturbed it ejects a 

 quantity of purple fluid which at one time was believed to be 

 highly poisonous ; and the harmless little mollusc was regarded 

 with superstitious awe by fishermen in most parts of the world. 



The Doris or Sea-lemon belongs to the Nudibranchs or Naked- 

 gilled Molluscs. It has no shell, and carries its plume-like gills 

 arranged in a rosette at the posterior end of its body. The Doris 

 looks very much like a lemon cut in half lengthwise, and is usually 

 some shade of dull yellow, though different species vary very 

 much in colour, some being pure white. Some Nudibranchs have 

 no special breathing organs, and respiration is carried on most 

 probably through the skin. Others breathe by means of feathery 

 or leaf -like gills, carried in tufts upon the back, and these are 

 often extremely beautiful in form and colour. 



