Hi Rita,
     I understand how the Wentletraps get confusing.  One thing I can tell
you straight away is the Epitonium lamellosum is not found at Sanibel.  In
my experience, the 5 most common Sanibel wentletraps are:
Epitonium angulatum,
E. humphreysii,
E. tollini,
E. rupicola,
E. multistriatum matthewsae
(roughly in that order- the first two are much more common than the last
three).  There are others but they are much rarer.  Of these five, it is
the first 3 that provide the greatest confusion (especially when the shells
have become at all worn).  If you find the shell is cream colored between
the white ribs (costae) it is more likely to be humphreysii.  Humphreysii
is also typically thicker ribbed than angulatum or tollini.  Though
humphreysii can have a slight angle to the ribs at each shoulder in a
pristine shell, angulatum's "angles" tend to be more pronounced (basically
squared rather than rounded).  Also an adult angulatum tends to be larger
than humphreysii (3/4-1 inch vs. 1/2 to 3/4 inch).  Although I have found
plenty of Juvenile angulatum and humphreysii to potentially confuse the
issue further, it is good to note that juv. angulatum tend to have very
extreme squared off shoulders.  Tollini, often confused with humphreysii,
is usually more slender, has strictly rounded costae, and doesn't get above
a 1/2 inch. Rupicola is unmistakable unless eroded to the point of losing
all color.  Typically the shell has clear brownish bands that set it
apart.  Multistriatum matthewsae is usually very small (<1/2 inch) and has
many ribs per whorl (>15).  This sets it apart from all the preceding
wentletraps.  I hope this information is helpful.  -Take care, Kevin