XVIII.—Records ofPotamopyrgus jenkinsi(Smith) in Scottish Fresh Waters over Fifty Years (1906–56)

Abstract

SynopsisThis note presents in summary the recorded occurrences ofPotamopyrgus jenkinsi(Smith) in fresh waters in Scotland over the fifty years since it was first reported. Apart from isolated occurrences in the Outer Hebrides, in the Caithness-Orkney area, and in the Borders—Solway area, the records appear to reflect a gradual dispersal (1906—56) from an origin on the Tay, over the Tay and Forth drainage areas, and thence perhaps through the Midland Valley to the west coast. This dispersal has been slower than the rate of spread of the same species through England and Wales earlier in the century, but has been rapid compared with the rates of dispersal assumed for other molluscan species.