Xiv INTRODUCTION. 



ternal coloring and marking which had characterized 

 their earlier periods. But although these differences, in 

 some instances, are sufficient to excite a considerable de- 

 gree of perplexity, yet there is always a certain appear- 

 ance by which the Conchologist will be able to distinguish 

 the genus and species by the shells alone; for every genus 

 and species has its generic and specific character, either 

 in color, work, or substance, which it almost invariably 

 retains in all its stages of growth, and varieties of form, 

 and consequently is thereby easily known and distin- 

 guished. 



Properties of Animals inhabiting Shells. 



These animals possess the power of extending or aggran^ 

 dizing their calcareous habitation or shell, and are also 

 enabled to repair Avhatever breaches this brittle dwelling- 

 may have sustained, by the turbulence of the tempestu- 

 ous ocean. The operation of enlarging aud repairing 

 their shell is supposed to be effected by a peculiar en- 

 dowment of the animal, which can at pleasure discharge 

 a viscous humor, and which readily becomes hardened 

 or consolidated, and soon acquires the consistence of the 

 rest of the shell. 



Many shells are covered with a cutaneous or skin-like 

 substance, called the Epidermis, which serves to protect 

 the beautiful colors and workings which are frequently 

 concealed beneath it. 



Customary itses to which Shells and their Inhabitants 



are converted. 



The principal benefit derived by man from shell-fish, 



appears to be in the way of food. Whole countries are 



known to have no other sustenance for weeks together, 



