CLAUSILIA. 171 



the plate on one side into a groove situated between 

 the inner plait and the columella, where it is detained 

 by the pressure of the body of the animal, leaving 

 the aperture free ; and when the animal withdraws 

 itself the plate springs forward by the elasticity of 

 its pedicle, and closes the aperture. This curious 

 structure, and also the plaits of the mouth, which are 

 intimately connected with it, are not formed until the 

 animal has nearly reached maturity. It is best exhi- 

 bited by breaking off the outer part of the aperture 

 to the distance of about half a whorl, when it will 

 generally be found free ; but in order to exhibit it 

 behind the columella in its natural position, when the 

 animal is exserted, it is necessary to kill the animal 

 in that situation (by drowning it), and then suffer it to 

 dry before the outer lip is broken off, and the pedicle 

 will thus become fastened to the side by means of the 

 dried mucus (of the body). It may, however, at any 

 time be relaxed by a little moisture, when it will 

 instantly resume its elasticity, and spring from its 

 attachment." 



It is probable that some of the Clausiliae are thread- 

 spinners. Mr. John Dixon, of the Leeds Infirmary, is 

 said to have seen "several individuals of C. rugosa 

 var. dubia suspended." — J.C., November, 1878. 



A. Margin of clansium entire. 

 I. Clausilia rugo'sa,* Draparnaud. Pl. IX. 



Body dark brown, or greyish-brown above, of a lighter colour 

 underneath, irregularly tuberculate ; tentacles short, thick (espe- 

 cially at their base), of a dirty brown with a tinge of slate-colour 



* Wrinkled. 



