L6 



POPULAR CONCHOLOGY. 



The power of forming shell does not appear 

 to be confined to the edge of the mantle, but 

 exists throughout its Whole extent: this has 

 been proved by removing part of \the shell of a 

 living snail, at a distance from the\ edge or lip : 

 the animal immediately sets about filling up the 

 gap, and effects it in the course of \a few days 

 by a succession of thin strata of liquid shelly 

 matter, which exude from that portion of the 

 mantle which has been laid bare. 



The regularity of the growth of many shells 

 appears to be interrupted at particular times by 

 changes which arise in the shape of the mantle ; 

 this is observable in several species, which ex- 

 hibit cones or spines projecting from their sur- 

 face, and which have been produced by the 

 mantle altering its form, and dividing into seve- 

 ral long slender branches. On these processes 

 shell is formed, constituting a row of hollow 

 spines, which are gradually filled up by suc- 

 cessive depositions of shelly matter, and event- 

 ually become solid; the mantle being then 

 withdrawn from them, proceeds in the form- 

 ation of new shell, branching out at regular in- 

 tervals into another row of spines ; and in this 



