Interesting thought Andrew - it brings up the question "what exactly
constitutes a common name?"  Before I say anything else, let me say
that my comments on common names will necessarily refer to english
common names, because that is my mindset.  I do realize that the same
shell I call a nutmeg or a jewelbox or an auger may have quite
different names in German or Spanish or Japanese, and those names may
or may not have any relevance to the english names.  In fact, it might
be interesting to hear some of the common names which apply in other
languages for species in some of the common families.  Anyway, in
reading Andrew's post, it struck me that Nautilus is clearly a common
name (in english), and is also a genus name.  There is no other common
english name for the animals in this genus.  Likewise for Octopus.
The names Unio, Chiton, and Murex are used similarly, though, unlike
Nautilus, they are used to describe species in a number of related
genera, not just the specific genus used as the name.  Some very old
books may refer to Murex as rock shells, but that name is pretty
nearly obsolete now as a general term.  In modern usage it applies
only to the subfamily Thaidinae (Thais, Purpura, Nucella, etc.).  So,
Murex, it seems, would qualify as an accepted common name.  On the
other hand, I am not as sure that Pecten qualifies as a common name.
Certainly a majority of collectors refer to members of the family
Pectinidae as "Pectens".  But we also speak of cowries as "Cypraeas"
and nutmegs as "Cancellarias".  Do Cypraea and Cancellaria qualify as
common names?  If not, why Pecten?  After all, there is the english
term "scallop" for the same group of animals.  Just offering a few
ideas here for consideration - when does a genus name qualify as a
common name?  Is it only when no other common name exists?  That
probably is not a good definition, as there are many families of
mollusks that have no common names at all, and by that definition
names like Trochomorpha and Stiliger would become common names.
Of course, there are many cases where the common name is a
translation of the genus name, or is at least directly derived from
it -  Nerite from Nerita; Olive from Oliva; Volute from Voluta; Cone
from Conus; Miter from Mitra; Tellin from Tellina; etc.  But this is
not quite the same as using the actual unadulterated genus name as
the common name.
 
Paul Monfils