I think the reason they did it this way is to have individual parameters which are metrically independent. Shell width and shell length are independent parameters. A change in one does not affect a change in the other. However, spire height and shell length are not independent, because spire height is a subset of shell length. An increase in spire height (independent factors remaining constant) therefore produces an increase in shell length as well. For two shells of a given length, an increase in shell width will increase the width-length ratio by an identical factor. Likewise, for two shells of identical aperture length (which for a Conus is essentially overall length minus spire height, or body whorl length), an increase in spire height will increase the spire-aperture ratio by an identical factor. For example, if the spire height increases by 32% (aperture length remaining constant) then the spire-aperture ratio also increases by 32%. This is ideally how you would like a ratio to work - if the numerator doubles, the ratio doubles. However, using the ratio of spire height to overall length, the situation is quite different, because a change in spire height (independent factors remaining constant) contributes to overall shell length. In other words, increasing the numerator of the ratio also increases the denominator, though by a lesser amount. Therefore an increase of 32% in spire height would NOT result in an increase of 32% in the ratio of spire height to overall length. Well, that's my guess. Whew! Paul M.