TUSK- SHELL. 147 



as to its true affinities ; by some being considered as a 

 true mollusk allied to the Limpets, by others as a worm 

 allied to the Serpulce. Anatomy determines it to be 

 rightly located by the former opinion, and yet the 

 possession of red blood, and some other peculiarities 

 belonging to the Annelida, indicate a curious relation- 

 ship with this class, so that we may consider it as one 

 of those interesting forms which link together two 

 great divisions of the animal kingdom. 



When the Tusk -shell is found alive, we rarely can 

 see more of the soft parts than a sort of white cushion 

 occupying the mouth of the shell, and occasionally 

 protruding or receding, with a little conical point 

 projecting from the centre of it. You might keep it 

 for weeks, as I have done, and see no more, by the 

 most assiduous watching, than this ; but at some fortu- 

 nate moment you might perchance see the whole foot, 

 of which this little cone is the extremity, thrust far out 

 of the cushion-like collar, when you would discern a 

 wide lobed membrane, fringing the base of the foot, 

 trumpet-like in shape, or resembling the blossom of 

 a convolvulus, with the thick and pointed foot pro- 

 jecting from its centre like a pistil. 



These sluggish white mollusks ordinarily live on 

 the muddy sea- floor, or burrow in it, where they devour 

 minuter animals, such as Foraminifera, and the spawn 



