INTRODUCTION. 



well here to advise those who are forming a collection to be 

 very particular in every practicable instance to have the shells 

 properly named at the time of purchasing; as it will save 

 much trouble, and materially assist in the attainment of the 

 desired object. To this end, recourse should be had to those 

 naturalist tradesmen, who unite the attainment and diffusion 

 of real scientific knowledge with their commercial pursuits. 



Supposing, however, that the person who desires to learn 

 the science, possesses a small parcel of unarranged and 

 unnamed shells, without any previous acquaintance with the 

 subject, the following introductory explanations, are drawn up 

 with the view of enabling him, without further assistance, to 

 obtain a general insight into its principles, equal to that of 

 those who have studied it long and laboriously. To effect 

 this, he must read them, carefully comparing the descriptions 

 with the figures referred to, and with the specimens which he 

 may have at command. 



After describing the nature of the science and defining its 

 objects, we shall proceed to explain the structure of those 

 objects, and the manner of their growth. We shall then enter 

 somewhat minutely into the principles of classification, the 

 distinctions upon which they are founded, and some of the 

 technical terms used to express them. After which we shall 

 pass through the arrangement of Lamarck, defining the general 

 divisions adopted under the terms of " Classes, Orders, and 

 Families" as far as they are capable of definition. The sub- 

 division of the latter into genera will only be entered into so far 

 as to enumerate the principal of them, the more minute de-^ 

 scriptions being reserved for the alphabetical part of the work. 



Let none be discouraged by the number of generic dis- 

 tinctions proposed and adopted in modern times ; for if well 

 defined, they will be found to facilitate rather than encumber 

 the science. The knowledge of species must be the foundation 



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