Hi Linda,
I also had some specimens of "Voluta claydoni", a slender, fragile white shell
from Australia.  They drove me nuts for a couple of years.  No-one I showed
them to had any idea what they were, and I pretty much exhausted the
literature on Volutidae.  I finally was able to identify them when I purchased
Barry Wilson's 2-volume set Australian Marine Shells.  The specimens I had
(and I suspect the specimen you have) were Benthovoluta claydoni Harasewych,
1987.  The reason it is not in the Poppe & Goto book is that it is not a
volute!  The genus Benthovoluta is classified in the family Turbinellidae,
believe it or not.
Regards,
Paul M.