L. F.  Chichester and Getz, L. L., ?The terrestrial slugs of northeastern North America?, Sterkiana, vol. 51, pp. 11-42, 1973.

H. E.  Quick, ?British slugs (Pulmonata: Testacellidae, Arionidae, Limacidae)?, Bulletin of the British Museum (Natural History), Zoology, vol. 6, pp. 103-226, 1960.