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V. 1 



ADVERTISEMENT. 



It is intended in the present work to give, as far as possible, a complete history of 

 the British species of Mollusca included in the order Nudihranchiata of Cuvier, together 

 with careful and detailed drawings of each. The latter are the more necessary on account 

 of the perishable nature of these animals and the impossibility of preserving them with their 

 proper forms and colours in museums. 



From the difficulties attending their study on this account, many authors, in treating of 

 the Mollusca, have entirely omitted the Nudihranchiata, and have confined themselves to a 

 description of the testaceous Mollusca alone, thus leaving a gap in the chain of affinities incon- 

 sistent with a proper knowledge of this sub-kingdom of nature as a whole. 



The authors of the present work confidently hope that they will be able, as far as the 

 British species are concerned, to supply this deficiency, and to give such full delineations and 

 descriptions of most of the species as may prevent any difficulty in their recognition by future 

 observers. By the kind assistance of their friends, added to their own researches, they have 

 been enabled to accumulate a large store of materials, but there are still several species 

 described by other naturalists which they have not met with. As the Society to whom 

 they are indebted for the publication of this Monograph have determined to bring it out in 

 Parts, extending over a period of four or five years, the authors hope yet to obtain many of 

 these species before its completion. 



For the purpose, therefore, of affording an opportunity of adding drawings and descrip- 

 tions of these from the living animals, it has been thought advisable to publish the species 

 promiscuously, adopting such a plan as will allow of their being arranged systematically on 

 the completion of the volume. 



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