The false Cancellaria operc is an interesting part of this hobby.  Not all
who collect shells and then try and sell them are necessarily well educated
about shells.  If you don't believe me take a look at some of the offerings
on eBay.  I love reading a description of shells that "I collected on
Sanibel Island," and the picture shows a bunch of beat up shells from the
Philippines.  Sometimes if you ask for an operc -- that is what you get,
just maybe not the right operc.  In years past I have received nerites with
Natica opercs carefully glued on cotton in the aperture as well as opercs I
know belong to other species of nerites.  This has never happen, I repeat,
never happened with the shell dealers now in business.  I once got a shell
(nerite) with a great looking, heavy, calcareous, white operc with heavy
horizontal ridges.  Sadly it was not a nerite operc.  I always hoped to
identify that operc and it is still around here some where.  Maybe
someday......

Tom Eichhorst in New Mexico, USA where it is presently snowing.