Despite Nat. Geo's great reputation and good intentions, this "definitive
answer" is a gross underestimate.  Fewer groups have been monographed in
the last 50 years than have been monographed.  The amount of new specimen
material available, both from private collectors and professional
expeditionary pursuits is staggering in all environments (land, freshwater
and marine).  I agree with Alan Solem's observation that any revisited
group of mollusks (Ok, maybe not strombids, cassids, volutids, etc.) goes
through the following:
 
The reviewer synonomizes, with the aid of the many more specimens available
today, a few to many old names which were coined mostly due to the lack of
adequate material.  However, this newly available material also includes
sometimes numerous undescribed species because collectors of all types are
more numerous, we are getting to more remote localities, collecting
techniques are more refined, better equipment, etc.  It has not been
uncommon to double the number of taxa in a given genus or subgenus based on
the new specimens.  So in short, there is usually an initial reduction in
the number of taxa followed by a sometimes great addition of species/names.
 
I personally believe that we have barely scratched the scratch on the
surface and even the oft 100,000 figure bantered about is low.
 
Kurt
 
 
At 08:41 PM 1/28/99 -0500, you wrote:
>With regard to the not entirely serious recent discussion on Conch-L of the
>number of living molluscan species, I offer this not entirely serious
>addition.  The most recent edition of the National Geographic (Feb. 99)
>provides a definitive answer: 70,000 (chart facing p. 23).