> David,
 
I'm going way beyond my expertise here but a couple of comments anyway.  First,
the varix can be close or far from the aperture depending upon how long ago it was
formed.  I have always assumed that each varix is a pause in growth; almost as if
the animal has said, "Okay, I've reached sufficient size to breed and whatever,
time to build up the edge a bit."  Or habitat conditions change or whatever.
Nothing anthropomorphic about my analysis!!  Both of my specimens of Phalium
glaucum are without any mid varix - the only thick area is the lip.  If your P.
glaucum does not have a thick lip (and it hasn't been broken and maybe ground
smooth) then you got a shell in a rare period of fast growth in between edge
formations.  These guys can grow shell amazingly fast and I'll bet they often hold
up under a rock or whatever and add a bunch of shell with the final stage the
addition of the lip.  The alternative would be to slowly and continually to
dissolve the lip and build the new lip.  Way too inefficient for mother nature.
 
Now about books.  The Wye book is nicely illustrated (except for the P. glaucum)
and although it has only 1,200 species illustrated, it does have some not shown in
other major, general shells guides like Eisenberg's or Abbott and Dance's.  The
last (the compendium) is the most popular and has just been reissued.  It has over
4,000 illustrations.  Eisenberg has only 2,500 or so but has a nice layout for
size comparison.  You might want to look for one of these.  The other books I
would recommend are "A Natural History of Shells," by Geerat J. Vermeij and "The
Encyclopedia of Seashells," by Dr. Gary Rosenberg.  The latter presents clear and
easy to understand information on shells - a "Conchology 101."  Very, very useful
and, I repeat, understandable - a rare thing in many books on so specialized a
topic.  Vermeij's book goes in to much more detail and pretty thoroughly covers
the how and why of the shell these mollusk characters carry around.  My problem is
I read it once, about 4 or 5 years ago and I guess I need to read it again to
refresh these aged brain cells.  I'm sure there are many other great books out
there (in fact I can think of several right now) but I think these form a solid,
general foundation for later excursions into specialized areas.
 
Anyway, thank you for bringing up this topic and getting me back into a shell
biology book.  I will start reading Vermeij again tonight and Rosenberg tomorrow
to see what light they can shed on your shell questions.
 
Tom Eichhorst in New Mexico, USA