Rarity
 
Everyone thinks others know what they mean when they say a thing is
rare.  I don't think that this is true.  My old dictionary gives one
definition is "Not thoroughly cooked" .  A lot of conversation about
rarity falls in this category.
 
The next definitions are "Not thick or dense"  (we hope this applies to
most of CONCH-L people); "Of an uncommon quality; usually excellent as a
person of 'rare charm'";  Seldom met with or occurring; very uncommon";
and "of a relatively small class as, a rare gem"
 
In defining rarity, time is an important factor.  What is rare once  can
become common.  What is common once can become rare.  Very old people
might consider mastedons common, but now most people consider them very
rare.  In mollusca, in Hawaii, Cypraea semiplota were once common in
shallow water, then for about 20 years no live specimens were found.
People had been diving for a number of years looking for shells before I
arrived in 1954.  One weekend a friend found the first recorded live
Cypraea rashleighana collected by a diver, and the next weekend I found
a second.  Later, if you looked in the right place, which was very
different from where they were found commonly years earlier, we found
Cypraea semiplota to be fairly available (you could see 4 or 5 in two
dives).  It is quite probable that people had looked at that same
location in the prior 15 years and didn't find any.  At times I am
convinced that these species were really rare (obviously some were left
to propagate).  I believe that this is true of other species that have
been discussed.
 
The definition of rarity should include geographic factors.  If are an
Eskimo (or Ross) looking for Cypraea moneta off the sunny coast of
Thule, Greenland you would consider them very rare.  If people only
lived in the environs of Thule, the consensus would be that they are
truly rare if not extinct and the local museums wouldn't have specimens.
 People, however, are distributed around the world (in unfortunate
numbers) and to many the species is common.  When Scuba was not
available, many species were rare that lived too deep in crevices to be
found by dredging.  Modern equipment has extended the capabilities of
finding things on the earth, moon or planets.  Other rare things will
become less rare.  This involves both time and technology.
 
Legislative actions (with enforcement) can cause species to become rare
so far as acquisition of a live specimen is concerned.  Again this is a
combination of time, geography and legislation.
 
In the instance of deep water species becoming more common, we may never
know whether or not they had truly been rare and had a population bloom
due to unknown reasons, or if they were always (very doubtful in
extending 'always' by billions of years).
 
Aloha,
 
Wes