Below you find some more shell related websites:

Royal Belgian Society for Conchology Belgian society (Dutch as official language) and publisher of the magazine ‘Gloria Maris
Belgian Society for Malacology Belgian society (French as official language) publisher of the magazine ‘Novapex!album-10
Royal Belgian Institute for Natural Sciences Museum of natural history with a nice department of seashells
Flanders Marine Institute Marine & coastal research institute with an extensive library
Arne Ghys A complete overview of Pectinidae and related families with maps and many excellent figures
French Society for Conchology French society, publisher of the magazine ‘Xenophora
Dutch Malacological Society Dutch society of shell collectors, publisher of the magazines ‘Basteria‘ and ‘Spirula
The British Shell Collectors’ Club Shell club from the United Kingdom
Spanish Malacological Society Spanish shell society, publisher of the magazine ‘Iberus’
Other parts of the world    
Conchologists of America Principal American Society
Auckland Shell Club Shell club from Auckland, New Zealand
Conchology, Inc. Commercial site run by Guido and Philippe Poppe showing among others an important Encyclopedia