necKL^cesgeas 



A^ERY large number of 

 species now to be described 

 constitute the sub - order 

 Monotocardia — the mol- 

 lusks that have only one auricle to the heart, a 

 single gill-plume (the left), one kidney, the nervous 

 system more concentrated, and mostly with a pro- 

 boscis. 



The Violet-snails (lantJdna), of wliich several 

 species are found washed upon our western shores, 

 are not natives, but their shells are so frequently 

 found in a fresh state, if not tenanted by the living 

 mollusk, that some general reference to them is 

 necessary. They are what are termed pelagic 

 species — living entirely at tlie surface of the sea, 

 where they feed upon the smaller species of jelly-fishes. 

 The destruction of Velella in this way led to the 

 supposition in the eighteenth century that lanthina 



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