Dear Sarah,
 
Seasons greetings.
 
Hope you are enjoying your break now that exams are done.
 
Regarding your question regarding Epitonium eburneum (Potiez & Michaud, 1838),
I quote in its entirety the species account for E. eburneum in Johnsonia,
Clench & Turner, 1951, "  It is impossible to tell just what this species may
be be as the poor figures could represent any of several forms.  The few
casual remarks regarding the diiferences between this and Epitonium lamellosum
Lamarck and Opalia australis Lamarck are far too superficial to be of any
significant value.  We suggest that it should be dropped from the list of
westtern Atlantic species."
 
In my personal experience,  the only specimens I have seen with this name,
could be referred to other  species , i.e. Gyroscala rupicola (Kurtz, 1860).
Without having more information regarding the material in your collection, I
couldn't comment further regarding an ID.
 
Hope this helps.
 
Sincerely yours,
 
Lenny Brown