CHAPTER V. 



CENSUS OF THE AUTHENTICATED DISTRIBUTION OF BRITISH 

 LAND AND FRESH-WATER MOLLUSCA. 



BY JOHN W. TAYLOR, F.L.S., 

 AND W. DENISON ROEBUCK, F.L.S. 



WITH the view of facilitating the labours of the numerous con- 

 chologists and others who are throughout the United Kingdom 

 assisting us in working out the detailed distribution of the British 

 land and fresh-water mollusca, and also of those who may here- 

 after be disposed to assist us by submitting specimens for 

 authentication and record, the following " census " has been framed. 

 It is strictly limited to " authenticated " records, that is, to such 

 as are verified by specimens which have passed under the 

 examination of the Conchological Society's referees. This pro- 

 cess secures uniformity of value in the results. 



The numbers are those of counties and vice-counties, a key 

 to which will be found at the end of the chapter. It will be 

 seen that the Channel Islands are denoted by the cypher " o " and 

 that they precede district No, i. The total number of counties 

 and vice-counties for which we have seen specimens is given 

 under each species. 



For the present the distribution of the varieties cannot be 

 given, and some of the doubtful species such, for example, as the 

 mythical Arion flavus are also omitted. 



Conchologists and naturalists generally are requested to aid 

 in filling up the gaps in the records by sending us specimens for 

 authentication and study. They will not fail to note how very 

 imperfectly the mollusca of Scotland and Ireland are recorded. 



