ABSTRACT
H. C. Watson was well aware of some of the problems associated with mapping species distributions in vice-counties, and in particular he realized that if the recording units could be made sufficiently small then some measure of the general abundance could be gleaned from the map. The south-western distribution of Porcellionides cingendus suggests that it prefers mild, temperate climates, and that winter temperature might be a limiting factor. But if this is so, it also raises the question as to how its distribution evolved after the ice age. The Biological Records Centre was to act as a focus for national distribution mapping schemes and the lack of cartographic facilities in Ireland meant that the Centre had to produce distribution maps for the whole of the British Isles. In 1981 the Directorate published an Atlas of the Seas Around the British Isles which has very useful maps of the distribution of economically important fish species.
