Thanks Paul, I was using the term mytilus fairly loosely, I should have said "a
member of the Mytilidae".  You remember correctly, my examples are white with a
golden periostracum. Are these Modiolus you suggest  world-wide, and are they
cultivated for food like the Mytilus?  I will look up the reference that Harry Lee
suggested also.  We recently purchsed a library card from the University of
Calgary, and while their malacology section is not large, I know thay have several
of the journals.
 
Paul R. Monfils wrote:
 
> Hi Nora,
> I don't have your original e-mail any longer, but if I recall correctly you
> said your mussel shell had a brown periostracum over a white shell.  That
> would suggest a species of Modiolus, rather than Mytilus (same family though).
> There are numerous species, and some can be difficult to separate, especially
> if you don't know where your shell came from.
> Paul M.