Let me add a point about Helicostyla, at least most species.  The
periostracal bands are called hydrophanous lines.  The periostracum is
structured differently on the bands than off.  When the shell gets wet, the
bands all but disappear.  Wet one and see for yourself, then blow on it
until it dries.  It's pretty cool.  The adaptive significance of this is
unknown, as is how the periostracum is put down.  Why would it be
beneficial to be somewhat unicolored in the wet season?  Or is this some
byproduct of something else we haven't even noted yet?

A few camaenids share this character.

Anyway, when storing or particularly displaying Helicostyla do NOT polish
them up with oil, etc.  You'll end up with nice shiney shells that look
totally different than it should.....no lines.  I've seen it happen to
exhibitors.

Kurt

>specimen of the large, beautiful emerald green Helicostyla portei, if placed
>in bleach for half an hour, will come out as white as an Ovula ovum.
>Placostylus hargreavesi has a beautiful, intricate pattern pre-bleaching;
>pure white afterwards.  Incidostoma confusum, a big operculate land snail
>from South America, is light brown above, dark brown below - until
>bleaching.  Then it is pure white, with a pink apex.  Likewise for many
>other land shells.  Helicostyla pan is multi-banded before bleaching.  After
>bleaching it is three-toned, white, tan, and chocolate brown, but with no
>banding at all.  Some Chysallis species have both axial and transverse
>markings.  After bleaching, tranverse bands only.  The pretty axial markings
>are in the periostracum.  So proceed with caution!
>Paul M.
>