Dear Alexandra,
Welcome to the list.  Be prepared for a lot of information.  If I read the
message correctly, you need guidelines on a shell collection.  I apologize to
the list for saying this again but I think this book is a good source of
info.  A Guide to Identification; Seashells of North America by
Abbott/Sandstrom.  It is 14 years old but has info. on collecting and shell
habitat and ....  If you ever visit North America it might come in handy.
Jordan *