The Conchological Society of Great Britain and Ireland

Measurement of samples of Discula turricida collected over a long span of time from Ilheu de Cima, Porto Santo, indicated that from around 1900 the mean spire height had decreased to a new stable value, the change being accompanied by a temporary increase in variance of shell shape. This change was possibly caused by an alteration in micro-climate following the construction of a lighthouse on the islet in 1900.