PUPA. 



slightly incrassated and reflected. A single tooth is fre- 

 quently observable just within the upper part of the 

 aperture. Some species have from three to eight teeth, 

 placed immediately within the aperture, and very various 

 in size and form. Others are decollated, i. e. subject to 

 an accident which is neither peculiar to the Pupae, nor to 

 land shells, but to which several marine shells are equally 

 liable; it consists in the falling off of the first formed vo- 

 lutions of the shell after the animal has arrived at its full 

 growth. The young shells of several species of this Genus 

 may very easily be and frequently have been taken for 

 Trochi, their form when only three or four volutions are 

 grown, being very like some Trochi. 



We have represented such species as show the greatest 

 variation in form that we have observed in the Genus. 



