The dilema of of the "validity" of various types of subspecific taxonomy
is an old one, and really, i think the question is largely moot: while
the concept of "subspecies" (reliably different,  reproductively
isolated populations  which clearly belong to the same species) seems to
be quite valid and useful on almost all levels - even if difficult to
determine in some cases - , the practice of calling different
combinations of color, pattern and form by "forma" or varietal names
does little harm within the context of a community of collectors.
Essentially, when properly used (ie, when a subspecific taxa **reliably
and consistantly** refers to a particular, readily identifiable
combination of features) it offers a short, concise way of
differentiating differnt forms of the same species - when you see the
designation "Chlamys opercularis linaeata", for example, if you are
familiar with the form an image is immediately brought to mind of an
opercularis with thin radiating lines of color on it: **much** easier
than saying "That form of opercularis that has the thin, colored ribs on
a paler background"!!  Also, some forms or varieties are due to factors
other than normal population dynamics - for example,
ecologically-determined combinations of form, microsculpture and
sometimes color or pattern: "ecotypes", and there are others which are
probably caused by recurring mutations or diseases.  While many form or
variety names cannot be defended on scientific grounds, to many
collectors they can be nevertheless useful, and can enhance the pleasure
one obtains by the pursuit of conchology (some folks only collect named
forms, for example!) as well as offering a "nickname" or short
designation for a certain combination of features.  Further, they come
in VERY handy when a subspecific taxa is elevated to specific level -
which is not an infrequent occurance, i might add: you don't have to
change your labels much at all: just cross out the name of the species
to which it was originally assigned, and voila, you have updated your
collection.

 From a chilly springtime in New Scotland,
Ross Mayhew.

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