PREFACE. Vll 



in the great fabric of the " Systema Na- 

 turae;" but in attempting to eradicate the 

 faulty parts, and to supply their place more 

 fitly, they have injured some of the main 

 supports, and have nearly involved the 

 whole edifice in ruin. 



The following pages are devoted to the 

 task of faciUtating the study of concho- 

 logy, on the method of the Swedish na- 

 turalist; and they are written under the 

 firm persuasion, that a material change is 

 dangerous even in speculative matters, 

 when the principle has stood the test of 

 general consent, and when the means of 

 reaching perfection are not yet, or, per- 

 haps, may never be, attainable. 



Among those who are willing to yield 

 submission to the judgement of Linnaeus, 



