ScHAEFF — On the Slugs of Ireland. 537 



B. — Margin of foot without transverse striae = A. hortensis, A. bourguignati, 

 A. intermedius. 



I. — Foot coloured = A. hortensis, A. intermedius. 



a. Wrinkles flat — A. hortensis. 



h. Wrinkles with conical spikes = A, intermedius. 



II. — Foot white = A. hourguignati. 



Arion ater, L. 



Liraax ater and L. rufus, Linnd, Syst. Nat. 1758. Arion empiricorum, Fdrussac, 

 Hist Moll. 1819. Arion ater, Jeffreys, Brit. Conch. 1862. 



(Plate LVI., figs. 10-16). 



Colour very variable, but generally either brown, black, or red, in adults ; 

 and either light red or yellow in young ones ; wrinkles very long behind middle of 

 mantle, and sharply keeled. Foot generally yellowish, but never white ; head and 

 tentacles dark violet. 



Synonymy. — Many Continental authors have adopted for this species Fdrus- 

 sac's (8) name of A. empiricorum, chosen by him because he thought a new name 

 would avoid the confusion arising from Linn^'s adoption of two designations, 

 viz. " ater " and " rufus " for varieties of the same species. According to the 

 British Association Code of Rules, however, which is observed by British zoolo- 

 gists, the oldest name or the one standing first on a list shall be used, irrespective 

 of the suitability of the name. 



External Characters. — This species is the most variable of om' Irish slugs. During 

 youth the number of variations are much larger than in adults, as they almost all 

 darken with age, becoming more uniform in colour. 



In Ireland I have up to now met with six very distinct varieties of the adult 

 slug, viz. brown, black, claret-red, salmon-red, olive, and black with yellow 

 sides. In some of these the foot may remain unaffected by the colour, whilst in 

 others the foot becomes more or less coloured too, but I think that is not a point of 

 any importance. The brown variety (Plate LVL, fig. 10) is perhaps the commonest 

 (in the gardens about Dublin, at any rate). 



The margin of the foot, in all these varieties, is transversely striated, by which 

 character this slug may be distinguished from all other species of Arion except 

 A. subfuscus. 



The wrinkles are useful in discriminating between A. ater and A. subfuscus. 



TRANS. fiOT. DT7B. SOC, N-S. VOL. IV., PAKT X. 4 F 



