NOTES ON ARION HORTENSIS, A. CIRCUMSCRIPTUS, AND THEIR ALLIES. 



BY T. D. A. COCKERELL. 



ALTHOUGH all the slugs considered in 

 the present paper were formerly referred 

 by British authors to Arion hortensis, there 

 are at least two very distinct species, and 

 possibly three or more. Arion hortensis and 

 A. circumscriptus (oi boiirguignati) differ in 

 so many characters, both external and 

 anatomical, that once known, they need never 

 be confounded. A. ambiguus, which recently 

 turned up in Dorsetshire, is so extremely 

 near to boufgin'giiafi that its validity as a 

 species must for the present be considered 

 doubtful. Lastly, A. celticiis, which occurs at 

 Brest, in France, may be expected in S.W. 

 England or S. Ireland- or at least may be 

 looked for, since it so resembles hortensis 

 that if it were common there it would not 

 be recognised as distinct without an examina- 

 tion of the anatomy. Whether, indeed, 

 A. celtiais is a distinct species seems ciuite 

 as doubtful as in the case of A. anihiguus, 

 but Pollonera has found anatomical characters 

 to separate it. 



I will proceed to give descriptive notes, 

 and a provisional classification of the forms ; 

 at the same time expressing the hope that 

 some of your readers will make further 

 research, so as to decide more clearly the 

 points at issue. 



No. 3. Sept., 1891. 



I.— Arion hortensis, Fer. 

 (irt) Subsp. hortensis, s. strict. 25 millim. long; 

 sole, pale orange ; back strongly rugose, 

 with elongate rugse, the sulci between 

 them dark ; back and mantle dark, 

 minutely speckled with pale yellow ; 

 sides with dark bands ; foot-fringe with- 

 out lineoles ; head and tentacles dark 

 plumbeous ; mucus pore distinct, mucus 

 yellow ; lateral bands of mantle fairly 

 straight, enclosing respiratory orifice. 



Described from three living specimens, 

 found by D. B. Cockerell at Acton, Middle- 

 sex, February nth, 1891. 



Form, fallax, Ckll., "Garner," 1886, p. 

 139. I found this variety again last 

 year at Headley Lane, Surrey, quite 

 common upon the beech trees. I have 

 placed specimens in the British Museum. 

 It is doubtful whether fallax can be 

 separated from var. subfusca, C. Pfr. 



Form. nov. albipes. A single immature 

 specimen was found with the type at 

 Acton, Middlesex, February nth, 1891, 

 by D. B. Cockerell. Length about 13 

 mill. ; like hortensis, but greyer, not so 

 rugose ; sole white ; no keel ; mucus- 

 pore well developed ; lateral bands of 



