Since my initial query, I came across this on the Web.  The reference in the
text to "IG Report" refers to "The Inspector General's Report on Plots to
Assassinate Fidel Castro>"
 
The photo shown with the text depicts some species of murex shell.
sj
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Other Assassination Plots Against Castro
 
At some time in 1963, Desmond FitzGerald came up with the
idea of killing Castro with an explosives-rigged sea shell. "The
idea was to take an unusually spectacular sea shell that would be certain to
catch Castro's eye, load it with an explosive triggered to blow when the
shell was lifted, and submerge it in an area where Castro often went skin
diving." (IG Report, p. 77)
 
Desmond ran down to the book store and bought two books on
Caribbean Mollusca, and was disheartened to find that none of
the shells indigenous to the Caribbean were spectacular enough to snare
Castro's attention, nor were any of them large enough to hold a sufficient
amount of explosive material. Furthermore, the midget submarine that would
be needed to place the shell had too short an operating range for the
operation (IG Report, p. 77)
 
Had FitzGerald been reading too many Ian Fleming novels? It's
been rumored that Fleming was actually consulted by the CIA to help develop
a "final solution" to the "Castro problem." Or perhaps FitzGerald was
involved in some of the MKULTRA experiments and conceived some of his
schemes while blazing on LSD.  At any rate, the exploding cigar trick ended
up on the drawing board, although it didn't leave the drawing board. The CIA
also considered hiding a machine gun in a phony TV camera and riddling
Castro with bullets. (14)
 
Your tax dollars at work.
 
(c) Copyright 1996 ParaScope, Inc.
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I wonder how they were going to make sure that Castro picked up the shell
and not some innocent conchologist--maybe one of our own?  In any event, add
this to the "hazards of shelling" discussed by this panel some time ago.
sj