Cameron, R.A.D., Jackson, N. & Eversham, B., 1983
A Field Key to the Slugs of the British Isles
Separately bound reprint from Field Studies 5 (1983) 807-824. A short guide with dichotomous and tabular keys to those species which can be distinguished without dissection - ie the following are not reliably distinguished: Arion ater/rufus/vulgaris(lusitanicus auctt), A. hortensis agg, Deroceras reticulatum/agreste, although useful field hints are often interspersed through the notes, but this makes it rather cumbersome.
The work is downloadable from the FSC website.
||Field Studies Council (FSC)
||All the Britsh species, but critical groups not explored.
||Line drawings accompany the text, two colour plates in the centre.
||In the field (also useful to examine in the Hand).
||Relatively straightforward, apart from the aggregate spp.