R. Tucker Abbott, in his classic book, Kingdom of the Seashell, stated
the following . . .
"It might well be said that there is no such thing as a rare marine
shell, since any species living today must have a large enough
population, certainly of several thousands of individuals, to sustain
the species".
Sooner or later, that population is going to be discovered, which is why
the rare shells of yesterday, with very few exceptions, are not the rare
shells of today; and the rare shells of today will not be the rare
shells of tomorrow.
Probably my worst shell purchase, from a strictly monetary viewpoint,
was the pair of Cypraea teulerei I bought in 1972 for $75.00 apiece.  I
thought I was getting a great deal because that was about half the price
dealers were asking six months earlier.  Today, with a bit more
experience behind me, I would realize that such a precipitous price drop
is a sure sign of the imminent demise of a "rare" species.  One year
after my purchase, gem specimens could be had for $15.00, and
subsequently the average price dropped to half that or less.  Shortly
thereafter (just to add insult to injury) I attended a shell club
meeting where the guest speaker brought with him a box of about 200
Cypraea teulerei, which he unceremoniously dumped out on the table, and
offered to members at $.50 apiece!

Paul M.