Hi Phred,
When I reattach Xenophora attachments, I use ordinary "white glue"
(Elmer's Glue-All, Sobo Glue, etc.).  Not the white "school glues"
however - they are water soluble after drying.  The PVA (polyvinyl
acetate) - based glues like those mentioned above are insoluble in
water, once dried.  Epoxy is stronger, but that isn't really an
advantage I don't think, because if you attach the item with a glue
that is a lot stronger than the shell, a bump will then result in
either the attachment itself breaking, or worse, a piece of the
carrier shell itself breaking off, still bonded to the attachment.
Most epoxies and other resins also turn yellow upon hardening, or
some time thereafter.
Obviously, the first step in reattaching a carrier attachment is
figuring out exactly how it was originally positioned.  There is
usually an impression of the attachment in the body of the shell
itself (though, if the attachment was not well bonded in the first
place, the impression may be rather small and indistinct).  Figuring
out which part of the attachment was actually bonded to the shell,
and exactly how it was positioned, can take a bit of trial and error,
and patience.  Once you get it right, it should fit very precisely
into the impression.  Therefore, there is virtually no gap to be
filled with glue, and only a very small amount of glue is required.
A wooden spring-type clothespin is good to hold glued pieces in place
until they dry.  Plastic clothespins are more lilkely to slip off,
possibly causing damage.  If a small amount of glue oozes out of the
gap when clamped, remove it before it has a chance to dry, with a
small, dry, soft bristle brush (a child's water color brush is
ideal).  Then, if you want to, you can brush some ordinary baking
flour around the glued junction.  This will adhere to any exposed
glue, and give it a dull (rather than shiny) appearance once the glue
dries, which is virtually invisible.  Excess flour can be brushed or
blown away after the glue dries thoroughly.
The original Xenophora mekranensis ( I don't have the author handy)
is a fossil form.  X. mekranensis konoi Habe is a still living
subspecies of the otherwise extinct X. mekranensis.
Paul M.
Rhode Island