XXV111 INTRODUCTION. 



cence continues in vigour, is partly absorbed, or 

 totally wasted. In this case, the hollow part will 

 be supplied with testaceous matter, secreted from 

 the body of the animal, till it is filled up even with 

 the interior surface of the shell. In the Strombus 

 genus, where the lip of the shell is often lengthened 

 (or divided) into a certain number of channels, 

 or fingers, the same thing takes place ; each chan- 

 nel is occupied by a corresponding portion of the 

 animal, endowed with the same secreting faculty 

 as the other parts of the body, and consequently 

 capable of adding to its groove, whenever it finds 

 occasion. The Strombus Lambis, or spider shell, is 

 a remarkable instance of this digitated appearance. 

 In the genus Murex, the mouth of the shell is 

 lengthened (more or less) into a beak or canal, con*- 

 taining a cylindrical organ, capable of contraction 

 and extension. This, according to some authors, 

 is used by the animal as a feeler, and occasionally 

 as a cable, to moor the shell to some solid body. 



The furrows, or ridges, met with in other shells, 

 while the whole of their interior surface is polished, 

 will be readily explained, when we consider the 

 formation of the animal. These furrows occur par- 

 ticularly in the bivalve shells, such as the scallops 

 (Pecten), the cockles (Cardium), &c. ; and when- 

 ever we meet with this peculiar organization, it will 

 be found that the animal partakes of the same con- 

 formation, the extremity or fleshy contour being 



