Genital morphology differentiates three subspecies of the terrestrial slug Arion ater (Linnæus, 1758) s. l. and reveals a continuum of intermediates with the invasive A. vulgaris Moquin-Tandon, 1855 Author Reise, Heike Author Schwarzer, Anne-Katrin Author Hutchinson, John M. C. Author Schlitt, Bettina text Folia Malacologica 2020 2020-03-13 28 1 1 34 http://dx.doi.org/10.12657/folmal.028.001 journal article 10.12657/folmal.028.001 545b2a3f-10d0-4c1d-8136-301d98a3d1d2 4615365 but should A. ater rufus be applied to the BR or to the FR morphotype? As detailed by VAN REGTEREN ALTENA (1963) , LINNAEUS’ (1758) description of rufus referred to his book on the Swedish fauna ( LINNAEUS 1746 ; but the implied Swedish occurrence must almost certainly have been Arion fuscus : ODHNER 1951 , VON PROSCHWITZ 1985 ), to German material described by ALDROVANDI (1644) , and to the work of LISTER (1685) , who described both British and French specimens. Because both BR and FR forms occur on the Continent, but FR or fr are almost unknown in Britain ( CHEVALLIER 1974 , ROWSON et al. 2014a ), greater certainty is achieved by selecting a British specimen as the lectotype. Also this choice follows Recommendation 74A of the Code ( ICZN 1999 ) in ensuring compatibility with the nomenclature of CHEVALLIER (1972 , 1974 ) and ROWSON et al. (2014a , b). Hereby we designate as the lectotype of Limax rufus Linnaeus, 1758 a now non-existing specimen amongst those described by LISTER (1685: 7) from “Amberry” in Yorkshire. Amberry is Almondbury, south of Huddersfield, which may still be pronounced as Lister wrote it and appears with spellings similar to Lister’s in contemporary documents ( SMITH 1961 , TAYLOR 1975 ). The illustration of “ Limax rufus ” ( LISTER 1685 : fig. 1 on tabula 2), to which LINNAEUS (1758) also refers (he originally indicated “ p. 1” but in the 12th edition—LINNÉ 1767: 1081—corrected this to “t. 2. f. 1”), is plausibly of an individual from this population, since foreign localities, but not British ones, are consistently included in the captions to others of LISTER’ s (1685) figures, and Amberry is the single British locality for the species mentioned in the main text. In any case, since the illustration does not reveal anatomical characters, it is better to associate the lectotype with the named locality, from which fresh specimens can be collected, than to designate an illustrated specimen of uncertain origin. (Recommendation 74E of the Code ( ICZN 1999 ) trumps Recommendation 74B, which applies only “other things being equal”.) It is unlikely that any of LISTER’ s (1685) specimens of this species survive. In 1683 he deposited a collection of specimens illustrated in LISTER (1678) in the Ashmolean Museum, and an accompanying letter promised more; so perhaps the specimens described in LISTER (1685) , the appendix to LISTER (1678) , followed them. Nothing of this collection is known to have survived ( MACGREGOR 2001 ). We associate our BR morphotype with A. ater rufus because in Britain the br haplogroup is widespread (combining information from COI and 16S sequences) whereas the fr haplogroup is known from only a single locality ( ROWSON et al. 2014a ). Furthermore, all reddish specimens of A. ater s.l. from Britain that we have dissected are BR, which agrees with the results of CHEVALLIER ( 1974 ) . Moreover, we have recently found the BR morphotype occurring commonly in Almondbury, now the type locality. In theory LISTER’ s (1685) red slugs might instead have been hybrids between BR and A. ater ater , or improbably early occurrences of presumably non-native species such as A. vulgaris or A. flagellus . These possibilities could be made irrelevant to the issue of taxonomy with the designation of an appropriate neotype, as is our future intention. Our Arion ater rufus ( Linnaeus, 1758 ) corresponds to ROWSON et al.’s (2014 a) Arion rufus and to CHEVALLIER’ s (1972 , 1974 ) A. rufus rufus .