INTRODUCTION. O 



of every system, and the greater their number, the more 

 necessary it becomes to subdivide them ; if, for instance, all the 

 species now known were to have been included in the 50 

 genera of Linnaeus, a single genus would have contained many 

 hundreds of incongruous species, in which case it would be 

 much more difficult to remember them, than if they were to 

 be divided into a far greater number of genera. Every well 

 marked division, however arbitrary its limits, tends to simplify 

 the subject, and to facilitate the researches of the student. 



NATURE OF THE SCIENCE. 



Conchology is the study of shells, viewed and described 

 as to what they are either in themselves, or in relation to the 

 soft, inarticulate animals which produce them, and of which they 

 form a part. These animals are called Mollusca, and perhaps 

 the best general description of them will be found in De 

 Blainville's " Manuel de Malacologie et de Conchy liologie." 

 The following is a translation, " Animal in pairs, the body and 

 its appendages soft, inarticulate (not jointed), enveloped in a 

 muscular skin, commonly called the mantle, which is extremely 

 variable in form, and has developed either within or upon it 

 a calcareous portion, consisting of one or several pieces, 

 commonly called a shell." 



The term Mollusca was formerly restricted to those soft 

 animals which were destitute of shells, although possessing 

 in other particulars, the characters described above, and it was 

 used in order to distinguish them from the Testacea, which 

 were covered or internally supported by calcareous parts. In 

 the system of Linnaeus, the soft portions are first arranged 

 under the general designation of " Vermes Mollusca,'' and de- 

 scribed without regard to the presence, absence, or character 



of the shells ; and then the shells are separately characterized 



b 2 



