Hi Joe,

A filed lip can range from a real hatchet job that you can spot from 6
feet away, to a work of art that is difficult to detect, even with a
good microscope.  First of all, the more you know about what the species
is supposed to look like, the easier it is to spot an altered specimen.
For example, some shells normally have a very straight lip (like Conus
kintoki), while others have a gently curved lip (Conus amadis), or a
strongly curved lip (Thatcheria mirabilis).  If you get a Conus kintoki
with a curved lip, or a Thatcheria with a straight lip, it has probably
been altered.  Almost all shells that have a lip will show fine parallel
growth lines over the surface of the shell, where successive layers of
shell have been added to the lip as the shell grows.  "Parallel" is the
key word here.  The growth striae will be parallel to one another, and
they should also be parallel to the lip.  On a straight-lipped shell,
the striae are straight, and on a curved-lip shell, they are curved.  If
the edge of the lip angles away from the growth lines, or cuts across
them, it is most likely filed. Many shells have a colored, or at least
darkened, border along the inside edge of the lip.  Turbans are a good
example.  If the colored band is narrower in some places than others,
the narrow parts are likely to have been filed.  As I said, there are
different degrees of "filing" (which incidentally may be done with an
actual file, but is more often done with sandpaper or a grinding wheel
of some kind).  "Commercial grade" cone shells, typically found in bulk
bins in tourist shops, are almost always filed, and obviously so.  They
just run the lip edge over a grinding wheel until any obvious chips are
smoothed off, and that's it.  The resulting lip edge is "flat" or
"squared off" rather than the normal sharp edge that a cone normally
has.  The next level of alteration is to grind off chips as above, but
then reshape or resharpen the lip edge so it isn't obviously flattened.
This is a bit harder to detect, but is still pretty obvious to an
experienced collector.  To someone who really knows cone shells, a
resharpened lip just doesn't feel right.  It doesn't have the right
degree of "sharpness", and often doesn't parallel the growth lines.
Also, with a good magnifier (which is a must for detecting filed lips),
you can see the scratches left by the file or sandpaper.  The third
level of lip doctoring will not be seen on an inexpensive shell - it is
just too much trouble for the monetary return.  But if you are buying a
Conus excelsus, beware!  Some suppliers are very adept at grinding away
chips, reshaping the lip precisely, making sure the new lip edge
parallels the growth lines, and then polishing away the fine scratches
left by file or sandpaper.  Such a shell can be difficult to detect,
just as some rare cowries with repainted patterns can be.  If in doubt,
show the shell to an experienced collector, preferably one specializing
in the particular family.
Another, similar problem is resharpened spines, on long-spined Murex
species, or other spiny shells like Guildfordia yoka or Spondylus
imperialis - or even a resharpened apex, especially on terebra shells.
Again, these are easily overlooked by a beginner, but an experienced
collector can usually spot them.  A resharpened apex can be spotted by
an abrupt change in color, a sudden loss of sculpture near the apex, and
an abrupt change in the spire angle.  Spines on a Murex nigrispinosus or
M. troscheli likewise taper uniformly from their base to their tip.  A
spine which abruptly changes angle of taper at some point, or which is
unusually short, with a greater angle of taper, is likely filed.  Such
spines and apexes may also be abnormally sharp, and will show the
typical scratches upon magnification.

Paul M.