1922. No. 5. ARIONIDAE OF NORWAY. 1 3 



A. Oviduct decidedly shorter than vas deferens + epiphallus. 



a. Receptaculum nearly always with a pointed end. Atrium band- 

 shaped, at least twice as long as it is broad. Arion circumscriptum. 



b. Receptaculum rounded. Length of atrium less than twice its breadth. 



1. Oviduct dilates downwards, gradually or suddenl}'. 



Arion subfusctis. 



2. Oviduct of uniform breadth. Arion interrneditis. 



B. Oviduct about as long as vas deferens + epiphallus, superior halt 

 slender, the inferior half conically dilated. Arion Jiortcnsis. 



Avion ater (L.). 



1758 Umax ater Linné, Syst. Nat., ed. 10, vol. i, p. 652, No. i. 



1758 — infus Linné, op. cit., No. 2. 



1767 — albus Linné, op. cit., ed. 12, vol. i, p. 1081. 



1803 — iitarghiellus Schraxck, Fauna Boica Würmer, p. 252, No. 3158. 



1819 Arion ctiipiricoruiit Férussac, Hist, des MoU., p. 60, pi. i, fig. 3. 



Diagnosis. External characters: generally 10 — 12 cms. long, in Norway usually 

 either black or white. Mucus generally colourless, tenacious. Without shield-bands (which, 

 however, sometimes appear in the \-oung, where anteriorly they are almost like parallel straight 

 lines, close to the mid line of the shield). Tubercles of the skin long, often compressed so 

 as to form sharp keels. 



Jaw: highly variable, but in larger specimens at any rate with some slender ribs at a 

 mutual distance of about their own breadth. 



Radula : mesoconus of the median tooth practically not constricted at the base and 

 shorter than the distance from the latter to the anterior edge of the basal plate. 



Reproductive organs : atrium often transversally constricted into an upper and a lower half, 

 the former always containing the large, conically rolled up ligula; free oviduct short, not at all as long 

 as vas deferens — epiphallus ; the broader branch of the genital muscle inserating at the oviduct. 



Historical systematics. Already before Linné the species was de- 

 picted and described by Martin Lister (Hist. Anim. Angl., 1678, p. 131, 

 pi. II, fig. 17I as Li)nax ater (ater — black). Later on a series of forms 

 has been described all of them undoubtedly varieties, but partiallv given 

 the rank as species. As to several foreign forms it is impossible to deter- 

 mine the boundary between species and varieties. In order to include some 

 of these so-called species, Férussac introduced the name Arion empiricornm 

 [empiriens — physician, according to its early use in medicine), which is 

 the most generally employed except in the British Isles and in the Scandi- 

 navian countries. 



Description. External characters (fig. i and Plate I, 1 1 Arion 

 ater, "den svarte skogsnegl", in some places even called "regnorm") is 

 the largest of the Arionidae not only of Norway, but of Europe, not seldom 

 surpassing 10 — 12 cms., this length, however, being the commonest in 

 adult, fully-extended specimens. Like Arion subfiiscits and Arion intermedins 

 it is capable of great contraction, especially when irritated, so as to assume 

 a semi-globular shape. Somewhat characteristic of this species is the un- 

 commonly large aperture of respiration. The foot-fringe, /. e. the brim which 



