iv INTRODUCTION. 
It may be desirable, in the first instance, to peruse the ex- 
planations of technical terms used in descriptions, and then 
to pass through the plates, comparing the figures with the 
list, and referring from the list to the definition of the names 
of the principal divisions found in the body of the work. 
A general notion having thus been obtained of the arrange- 
ment of the principal forms, the learner may proceed to 
take a shell from the drawer; if it be a bivalve* shell, he 
will know that it is included in the class Conchifera ; if a 
multivalve, he will find its place in the class Cirripedes ; 
all his shells may thus be arranged in classes. Proceeding 
with the smaller divisions, the shells composing a class may 
be divided into orders by a similar process, always taking 
care to turn to the definitions, and to examine the shells. 
When, by further carrying on this operation, the shells are 
arranged in families, one at a time may then be compared 
with the figures of the genera contained in the family to 
which it belongs, and a little careful examination will pro- 
bably connect it with some generic form. The definition 
of the word must then be turned to, for purpose of ascer- 
taining whether the shell agrees with the description of the 
genus which it is thought to resemble. If, for stance, the 
shell having a row of little notched teeth on the hinge, has’ 
been placed in the family of Arcacees, and on further com- 
parison with the figures, it is observed that the hinge-line is 
straight, and that there is a flat area behind it, the learner 
will imagine it to resemble the genus Arca, and will turn to 
the definition of the word, to find whether the description 
agrees in other respects. Thus, comparing shells with 
figures, and the explanation of plates with the definition of 
* The Word Bivalve, has been inadvertently omitted in the text, but will 
be found described in the list of Errata. 
