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A TREATISE 



MALACOLOGY; 



SHELLS AND SHELL-FISH. 



PART L 



A GENERAL SURVEY OF THE TESTACEOUS BiOLLUSCA. 



CHAPTER L 



INTRODUCTORY OBSERVATIONS. THE JIOLI.USCA IN GENERAL. 



THE CHARACTERS AND ANALOGIES OF THE THREE PRI- 

 MARY DIVISIONS OR CLASSES; NAMELY, THE ACRITA, THE 



RADIATA, AND THE TESTACEA. NOTES ON THE BIKLIOGRAFHY 



AND THE EXISTING CLASSIFICATIONS OF THE LATTER. 



(1.) In our last volume, we completed the survey of 

 those great divisions of animals which, from possessing 

 a bony skeleton, are called the Vertebrata. Our pre- 

 sent treatise will be devoted to a far more numerous, but 

 less interesting, assemblage, — namely, the Mollusca, 

 or soft animals. These, with few exceptions, are 

 either inhabitants of the ocean or of fresh waters. The 

 majority are little known even to naturalists ; and 



