There is no correct way. Like Jose said, you just have to explain how you
did it. I always count along the suture: at the starting line of Verduin,
there is already 1 complete revolution, or 1 whorl. If you are consistent,
in the final tally suture counting will always give a half a whorl more than
the "Verduin method" (he wasn't the one who originated it).

If you don't care about the total number of whorls, but only care about the
whorl numbers with respect to the aperture, then you can count them starting
at the aperture. The body whorl is 1, the penultimate whorl is 2, so on.
This is useful if you are working with tall shells. See my paper: Örstan, A.
1999. Drill holes in land snail shells from western Turkey. Schriften zur
Malakozoologie 13:31-36.

~~Aydin
http://snailstales.blogspot.com
http://home.earthlink.net/~aydinslibrary/

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