21 8 Shell Life 



average length is about 1 inch, but the breadth is 

 less than seven-tenths. It is a rare shell, restricted 

 to the north of these islands in from 7 to 80 fathoms, 

 but most of the specimens have been taken from the 

 stomachs of haddocks. 



We have seen how the various species of Natica 

 partially envelop the shell in folds of the foot and 

 mantle ; in the next species the shell is completely 

 hidden by the mantle. 



The Transparent Marsenia (Marsenia perspicua) is 

 ear-shaped, with a very small spire, but eleven- 

 twelfths of the whole consists of the body-whorl, 

 which is almost flat. It is exceedingly thin and 

 transparent when fresh, but becomes less clear in 

 dying and loses a little of its form. The animal, 

 which is much laro^er than its shell, varies a crood deal 

 in colour from white to yellow or orange, with spots 

 and blotches which vary to contrast with the 

 ground colour. There is a pair of long awl-shaped 

 tentacles, with black eyes at their base only visible 

 from below, or when the creature swims inverted at 

 the surface. The ground colour and the markings 

 are examples of protective coloration, for the 

 creature feeds upon Compound Ascidians and its colour 

 assimilates to that of its food, whilst its markings 

 resemble the common openings of their colonies. Years 

 ago Mr. Peach devoted a good deal of time to a study 

 of this creature, and found that it resorted to patches 

 of LrptocliniiifYh gelatinositm, as he thought for the sole 

 purpose of excavating a pit in which to deposit its eggs. 

 Professor Herdman, however, a few years ago called 

 attention to the fact that Marsenia fed chiefly upon 

 Leptocliniiin, and that its colouring was protective. 



