S78 Mr, Miller 071 the Freshvater and Landshelh [May, 



discovered, in the year 1814, the valve^ike appendage which 

 turbo larainatus and nigricans possess. When Dr. Leach visited 

 me in 1815, I pointed it out to him, which he considered as a 

 new and interesting discovery. The Doctor furnished me with 

 several other reversed shells to facihtate my further researches 

 on this peculiar organization, and informed me subsequently 

 (when in Paris) that M. Drapernaud had noticed the valve-like 

 appen dage, and from it derived in part the character of his new 

 genus Clausilia. This information deterred me at the time from 

 further inquiry; yet as I have subsequently found that M. Dra- 

 pernaud seems at a loss concerning the use of this valve ; and 

 M. Cuvier, in his Regno Animal, vol.ii. p. 409, states, " de cette 

 petite lame, on ignore I'usage dans I'animal vivant ; '* I will here 

 venture to add the opinion which I have myself been led to form 

 on this subject. 



Independently of the various contrivances which Nature has 

 resorted to for the protection of the otherwise easily vulnerable 

 raoUuscee, it has taken peculiar care to guard the apertures of 

 many univalves from the intrusion of enemies. Hence the aper- 

 tures are sometimes peculiarly contracted, and provided with 

 numerous folds and teeth. Other molluscae have a calcareous 

 operculum, permanently affixed, which increases in thickness, 

 and enlarges on a depressed spiral plane, as the opening of the 

 shell extends with the growth of the animal thus continually 

 assimilating to its size, and when the animal retreats, excluding 

 it completely from all external intrusion. In the clausiha, 

 Nature has combined the protection afforded by means of con- 

 traction and folds, and also added an o[)ercular appendage. 

 The inhabitants of the Clausilia, when nearly full grown, 

 secretes a thread-like, elastic, calcareous filament, one of whose 

 ends is affixed to the columella. This filament makes a half 

 spiral turn round the columella insinuating between its folds. 

 When the animal finishes its shell, and completes the aperture, 

 it secretes at the unattached end of the filament a spoon-shaped 

 calcareous lamina conforming at its margin to the contour of the 

 aperture. The lamina is somewhat smaller than this, and its 

 margin is rounded. Its adhesion to an elastic filament enables 

 the animal to push it when it comes out of its shell against the 

 columella, and the same elasticity closes it, on the inhabitant 

 retreating, thus securing it from intruding enemies. Thus 

 then this valve may be compared to a door provided with an 

 elastic spring. The elasticity of the filament may be restored to 

 its full power by some times immersing it in water, as 1 have ascer- 

 tained in sections made with a view to this inquiry. 



20. Turbo juniperi. On mountain hraestone rocks. 



21. Turbo muscorum. In moss. 



22. Turbo sexdentatus. Leighdown. 



Observation, — ^The above three species belong to Drapernaud's 

 genus Pupa. 



