Thanks to David, Aaron and Art for their insights.  On my lunch hour I took a
surf through the Conch-Net and read Gary Rosenburg's articles on shell names
(Navigating Libraries and What's the good name).  Those articles are
eye-operners all right.  Obviously the answers take long research and access to
much published material.  I thought fossil taxonomy was a "dog's breakfast" but
molluscs seem to be a challenge in their own right.  I don't think I'm such a
purist that I will pursue the answers to the nth degree.  I'm a picky person at
heart and like everything to be in it's proper place, but I think I'll try and
relax a little and not get too concerned about name vagaries.  After all, a
shell is just as beautiful by any of it's myriad names.
Nora Bryan
Calgary, Alberta
CANADA
 
David Campbell wrote:
 
> >Take the common shield limpet  - in Abbott's North American Seashells
> >(1955 edition) and in the Eisenberg book (1981) it is shown as Acmaea
> >(Collisella) pelta with Collisella being the subgenus.  Other books such
> >as my more recent Audubon guide list the species as Collisella pelta.
>
> Recent examination of the type species of Acmaea has show it to be very
> distinctive, meriting separation from almost all other limpets.  Gary
> Rosenberg's Encyclopedia of Seashells gives more details and references for
> extensive details.  In general, the newer references will reflect more
> recent discoveries, although the quality of the reference must be kept in
> mind.
>
> >How would you (an experienced shell collector) label my above example in
> >your collection.
>
> Collisella pelta
>
> >I have noticed lots of shifting around of families also.  Is there any
> >publication that lists all of the latest commonly accepted mollusc
> >families.  I notice this changes from publication to publication also.
> >Is there even any consensus?
>
> Part of the problem lies in new discoveries.  Both closer examination of
> the animals and review of old literature and type collections may result in
> discoveries that show that our current classification is incorrect.
>
> The other problem lies in varying opinions as to what should be called a
> genus, family, etc.  Some people have broader concepts, some narrower; some
> people think a particular feature is very important and others less so.
> Also, there is not agreement upon the philosophy of classification.  Some
> people think a taxonomic unit should include all the descendants of a
> particular common ancestor whereas others will accept the possibility of
> recognizing one taxon as descending from another.  For example, current
> evidence suggest that the cones evolved from the turrids, so that some
> turrids are actually more closely related to cones than they are to certain
> other turrids.  Some people would therefore want to split the Turridae into
> multiple families, one of which would be the Conidae, and the whole group
> would be known as Conoidea.  The old "Turridae" would no longer have any
> formal status.  Others are willing to keep the term Turridae, with the
> acknowledgement that it does not include all the descendants of the
> ancestral turrid because it excludes the cones.
>
> Thus, updating your labels will be a continual necessity, though hopefully
> they are getting more accurate each time.
>
> David Campbell
>
> "Old Seashells"
>
> Department of Geological Sciences
> CB 3315 Mitchell Hall
> University of North Carolina at Chapel Hill
> Chapel Hill NC 27599-3315
> USA
>
> 919-962-0685
> FAX 919-966-4519
>
> "He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
> Gold Bug