Is the semi-slug Vitrinobrachium breve (A. Férussac, 1821) (Gastropoda: Vitrinidae) really new for Belgium? A historical investigation

Recently, the first sightings of the semi-slug Vitrinobrachium breve have been reported in Belgium. However, this species was probably already present in the east of the country a century ago. We present a historical investigation starting from an illustration in a book by W. Adam on Belgian land molluscs published in 1960. The depicted shell was presented as that of the semi-slug Eucobresia diaphana (Draparnaud, 1805) and was collected in 1923 in Malmedy. We show it most certainly belongs to V. breve. We also discuss the halo-effect hypothesis of an authoritative work in long-term identification errors and the historical biogeographic implications for these two species.