Some very interesting comments.  Here's a twist.  Rare could also mean, no
one is aware or cares.  Here's a shell that exists in eight museum
collections and probably no more than half a dozen private collections.
It's never been offered for sale.  It's a Cerithiopsis, so who cares?

http://z14.invisionfree.com/Conchologist_Forum/index.php?showtopic=734
Marlo
merritt island, fl

Mon 10/13/2008 7:01 PM; Marlo wrote:

I guess "rare" is a matter of perspective.  If you collect by purchasing,
then I guess rare is when you can't find what you want for sale.  If you
trade, I guess rare is when no one has what you are seeking.  If you collect
in the field, rare is when you're lucky to find a species once in 2-3 years.
I don't think rare relates to presence in nature.  Shells living in
difficult to reach locations or protected areas might be plentiful, but just
not available in the market place.  As several people have commented here on
Conch-L, some very common shells are rarely offered by dealers.  For
collectors who rely upon dealers, that makes them rare.

By "rare," most books mean the species is in a habitat difficult (or
unprofitable) to reach (or unknown) and few come to market.  I guess "rare"
would also apply to those endemic species that are over collected to near
extinction or in locations like thermal vents that are virtually
inaccessible.

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