69 

 THE NON-MARINE MOLLUSCA OF FRIESLAND. 



By F. H. SIKES, M.A. 



(Read before the Society, November loth, 1900). 



The distribution of land and freshwater shells in Friesland being, so 

 far as I could make out, entirely unknown or at any rate unpublished, 

 it seemed a good district to visit this summer, and though the results 

 are a trifle disappointing — forty species, with some interesting varieties, 

 were all that I managed to find — I have tabulated them for the 

 benefit of anyone that may hereafter intend to make a more lengthy 

 and systematic survey of the country. 



The Friesland meres cover about 50,000 acres, ten times the size of 

 the Norfolk Broads, and in the 600 square miles, wherein they are to 

 be found, there is the most intricate network of waterways imaginable. 



Over the greater part of these I sailed during the sixteen days I 

 was abroad, and took soundings whenever there was a chance of 

 finding anything, but for all practical purposes I might have confined 

 myself to Heerenveen, as every species but five existed there. 



The reason for the paucity of land shells is not far to seek, as most 

 of the country is partially, and sometimes completely, water-logged. 

 Heerenveen, however, proved to be a little oasis in a watery desert, 

 and closer search than I was able to devote may turn out more than 

 the thirteen new species that resulted fi-om the two days 1 was there. 



Owing, also, to a wreck in the middle of a large lake, which nearly 

 brought my shell-collecting to a summary close, I was unable to visit 

 a likely wooded district near Stavoren. 



The freshwater shells are generally the same throughout (with 

 varieties) as the canals run one into the other and rivers are non- 

 existent. 



Succinea obloiiga, which may be considered the best discovery, 

 occurred plentifully in a marsh at Heerenveen, thereby differing con- 

 siderably from its habitat in Georgenthal, Thuringia, where I found 

 it far from water in two disused quarries. 



Dreissensia polyuwrpha occurred at Grouw, where there are 

 timber-yards, and may, I suppose, be considered a Russian import ; 

 it seems to have spread pretty freely and most favoured the shells of 

 Anodofita cygncea. 



Perhaps it would be well to add that I am indebted to Mr. J. W. 

 Taylor for verifying or altering my conclusions, except in the case of 

 the slugs, which I was unable to send. 



