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CHAP. XXI. 



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MOLLUSCA WHELKS. 



The Whelk and its Varieties. Structure and Instincts, &c. 

 The Limpet. Structure, &c. 



THE bivalve molluscs are far from being the only 

 members of the group they belong to which attract 

 the attention of the visitor of the sea-shore. 

 Numerous specimens of the second of the two 

 groups into which the molluscs are divided pre- 

 sent themselves to his notice. This second group 

 is, as already mentioned, called, the Encephala, 

 and embraces all the molluscs furnished with 

 heads. The group is itself farther subdivided into 

 three classes in accordance with certain modifica- 

 tions of their locomotive organs. 



The first of these three classes is that of the 

 Pterapoda, a term which signifies " wing-footed," 

 and which comprehends several species of 

 molluscs of small size, specimens of which are so 

 little likely to come under the reader's notice, that 

 it is unnecessary to refer to them in a particular 

 manner. We shall presume therefore that our 

 reader's attention is given to the second class of 

 molluscs, which are called Gasteropoda, or belly- 

 footed animals. Of these every rocky sea-shore 



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