^ecklace-shells and Winkles 219 



We luive had many opportunities for checking 

 Herdnuin's observation, and can fully endorse it. 

 The gelatinous semi-transparent body of the mollusk 

 so closely matches the ascidian that it is difficult to 

 see it, and there is no doubt that the likeness protects 

 it from those creatures that would prey upon it if 

 they could see it. It is probable that the creature 

 and its shell have been greatly modified by its mode 

 of life. It was necessary at first to hide the shell 

 beneath the spotted mantle, then it would be 

 gradually flattened out so that the mollusk's back 

 did not rise so high above the ascidian, and when the 

 resemblance between the two creatures had become 

 sufficiently strong the shell w^ould no longer be 

 necessary as a protecting shield — therefore it would 

 be reduced to its present filmy texture. It is not a 

 common species, as it occurs chiefly in deep water 

 — down to 90 fathoms — but may be found on the 

 recess of the spring tides on the vertical faces and 

 under-sides of rocks and boulders where the 

 Leptocliiiiiiin colonies are. 



The Velvet-shell (Veliitina kevvjata). There is a 

 general resemblance between this mollusk and the 

 last, but though the flaps of the mantle 

 are turned over the shell the latter is not 

 hidden. Its name is due to the character 

 of the thick pale brown epidermis, which 

 is distinctly velvety. The animal feeds ^^'^^^-^^eii 

 upon Alcyonium and other zoophytes, and is found 

 on stony ground in the laminarian and coralline zones 

 (from 1 to 50 fathoms) all along our coasts. 



The Hairy-Keel Shell {Trichotropis horealis) is a 

 beautiful little shell with a superficial resemblance to 



