INTRODUCTION. 



SINCE the publication of the first volume of this work 

 I have made two more dredging- excursions to the 

 Shetland Isles, a district which is by far the most 

 interesting that I know of for the further investigation 

 of the British Mollusca. In the interval I revisited the 

 South of France, and also went to the Hanse towns, 

 Denmark, Sweden, and Norway, for the express purpose 

 of examining public and private collections of Euro- 

 pean shells, and especially the types of species described 

 by O. F. Miiller and subsequent writers on Scandinavian 

 conchology. Every naturalist will appreciate the ad- 

 vantage of such an undertaking, being aware that our 

 own fauna or flora cannot be properly studied apart 

 from that of the rest of Europe. These preliminary 

 remarks are offered to explain the cause of delay in 

 the appearance of the present volume, and likewise to 

 express my grateful acknowledgments for the kind 

 welcome and aid which I received from all the leading 

 zoologists in the countries above mentioned. Nor ought 

 I to omit a renewal of my thanks to many of my own 

 countrymen, who have again most liberally placed their 

 collections at my disposal and favoured me with valu- 

 able communications. I will now endeavour to profit 

 by the opportunities I have thus enjoyed, in extending 

 the list of our native Testacea, as well as in revising the 



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