INTRODUCTION. V 
words, the student may soon complete the arrangement of 
the few shells he is supposed to possess. It may then be 
desirable to pass through the system, with a view to as- 
certain whether the collection contains an example of each 
of the principal divisions; if not, they may be procured at 
a small expense; and then, by all means, let a collection of 
genera be formed as complete as possible. It may be as 
well here, to advise those who are forming a collection, to 
be very particular in every practicable instance, to have 
the shells properly namea at the time of purchasing ; as it 
will save much trouble, and materially assist in the attain- 
ment of the desired object. 
Let none be discouraged by the number of generic dis- 
tinctions created in modern times ; for, if well defined, they 
will be found to facilitate rather than to encumber the 
study. ‘The knowledge of species must be the foundation 
of every system, and the greater the number of species, 
the greater is the necessity for systematic distinctions. If, 
for instance, all the species now known, were to have been 
included in the fifty Genera of Linneus, a single genus 
would have contained many hundreds of species, and it 
would be more difficult to remember them, in that case, 
than if they were divided into ten times the number of 
genera. Every well marked division, however arbitrary its 
limits, tends to simplify the subject, and to facilitate the 
researches of the student. 
