Could be an English Dictionary vs American Dictionary thing.  For example a lot
of us Canadians use the English spellings of many words (example - Color vs
Colour, Check vs Cheque, Centre vs Center)  There are other English words where
we use the American spelling such as Tire vs Tyre.  If someone has an English
Dictionary vs an American one maybe they could shed some light.

Nora
Calgary, AB
CANADA

"Monfils, Paul" wrote:

> Andrew,
> I think you are suffering from a case of taxonomia!  The oldest name is the
> right one??  That works in taxonomy, but not in common english; otherwise we
> would all be speaking Olde English :-)   I think "mollusk" is still in
> commonest usage among the general population, while "mollusc" is usually
> used by those of a more scientific bent, presumably because it is derived
> from the phylum name Mollusca, which does NOT have any alternate spellings.
> Paul M.