Activity of different species of land-snail on surfaces of different inclinations

Observations on active snails at night give some support to the suggestion of Cain (1977) that there is a tendency for high-spired snails (other than burrowers) to prefer vertical surfaces when crawling, and for tbose with disc-like shells to prefer horizontal ones. Those with more-or-less globular shells show little preference. The absence or rarity of shells which are both tall and wide in most faunas may be due to a scarcity of surfaces of a rather narrow range of inclinations that would be appropriate to them. The overlap of more-or-less globular shells with both high-spired and disc-like ones is probably due to the preference of the globular ones for live herbaceous vegetation which is not favoured by the others.