Patty neglected to point out the main difference between shell books (and
shells on stamps) and the shells themselves : the former will always
decrease in number while the latter will increase. Dealers often say things
like 'now hard to get' to try and boost interest, but ultimately they are
selling something whose value is an inverse function of the number of
examples known. What price Conus milneedwardsi now? 20 dollars a piece here
in Japan; I can remember when they were 1000 or so, and I am a mere youth.
On the other hand, a full, original set of Conchologica Iconica went for
the equivalent of 2000 dollars thirty years ago; think five times that now.