When I first got R, K & K's Manual of the Living Conidae, I was
surprised by the fact that they compared Width (Maximum Diameter) and
Spire height to Aperture length rather than to shell length.

The aperture length is somewhat hard to define in many families but is
clear in R I & K as defined as axial distance from the suture at the lip
to the anterior tip of the shell.  For other families, the start of the
anterior canal and end of the aperture is ill defined and open to wide
interpretation by the person making measurements.

There are three things that are fairly defined to use in relative
measurements:  Shell length, Maximum width, and Spire length.  Why
wouldn't they have used these for ratios?

We are currently working on Mitridae, and make comparisons of width and
spire to shell length.  The canal length is mostly poorly defined so the
aperture length is therefore not well defined where there is a definit
canal (shown by change only in outer lip shape usually).  Any comments
on these ratios?
--
                     Aloha from Wesley M. Thorsson
Editor of Internet Hawaiian Shell News, a monthly Internet Publication
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