MOLLUSC A. 



THE Molluscous animals to which our attention is to be 

 directed in this article, formed, for a long period, two dis- 

 tinct objects of study. The naked species were considered 

 as constituting a particular group, to which the term MOL- 

 LUSCA was in a great measure restricted ; whilst the shelly 

 species attracted a large share of attention, being known as 

 objects of study by the term CONCHCXLOGY. Of late years, 

 however, this kind of systematical separation of the naked 

 and shelly species has been supported by few advocates, 

 whilst those who have urged the propriety of their union 

 have not only been numerous, but acknowledged as the 

 intelligent and successful investigators of nature. In con- 

 sequence of these changes, which have taken >place in pub- 

 lic opinion by the introduction of more correct notions of 

 the principles of classification, we have in [this edition of 

 our work, resolved on incorporating the articles MCOLLUS^A 

 and CONCHOLOGY, suppressing the latter term as unneces- 

 sary. Indeed, in a physiological point of view, there is no 

 definite boundary between the naked and the shelly species, 

 many of the reputed naked species having shells concealed 

 under their integuments, while in many of the shelly species 

 the solid plate or shell can only be reached by removing 



