INTRODUCTION. 



THE division, or branch of natural history on which thii 

 work treats, is called Conchology, and comprehends the 

 study and history of all animals which are testaceous, or 

 with shell coverings; and not only includes those of the 

 sea, but also those of rivers and land. 



Testaceous animals are such as have a stone-like, cal- 

 careous covering or habitation, in which the animal, 

 otherwise naked or fleshy, lives included and protected. 



All animals inhabiting shells are exsjhiguinous, that is 

 to say, they have no blood, like other animals ; and, unlike 

 them, are destitute of bones; but they are endowed with 

 a heart, lungs, mouth, and other organs adapted to their 

 nature. 



It is perhaps necessary to prepare the young Concholo- 

 gist with the knowledge, that all shells, in their various 

 stages of growth, assume very different appearances: in 

 the younger ones, the shell is usually fragile, thin, and 

 semitransparent, and generally unprovided with those 

 ribs, tubercles, ramifications, and denticulations, which 

 are manifest in those of maturer growth ; the adults, how- 

 ever, as they advance to old age, become more thick and 

 ponderous, and are remarkable for the callosities which 

 cover their surface; they also lose that brilliancy of ex- 



