thumb|Counting gastropod whorls. In this example a [[gastropod shell|shell with 3¾ whorls is shown, with the fourth whorl expanding more rapidly than whorls 1–3. increasing whorl counts by one-fourth.
Further reading
- Solem A. (1983) "Lost or kept internal whorls: ordinal differences in land snails". Journal of Molluscan Studies 49(supp. 12A): 172–178.