Now let us enumerate the species of land and freshwater shells to be found, (all but two) in England, and most of them in Ireland or Scotland.
Arion ater is a large (3 to 5 inches) and common slug, usually black (whence its name ater), but also red, brown, or white. In some varieties the foot-fringe is orange. When irritated it contracts into a hemispherical lump. A few chalky granules under the mantle are the representatives of a shell. See the illustration of three specimens on [p. 31]. That hole in the mantle is the breathing orifice, and its forward position is a characteristic of the group Arion. The body of slugs is kept moist by a constant exuding of slime from a gland in the tail.
Three specimens of Arion ater, showing tentacles, breathing orifice, and slime gland.
Arion subfuscus (i.e. somewhat tawny). Smaller (2 to 3 inches) than A. ater, grey or yellowish, with usually a dark stripe on each side. Foot-sole white, and its fringe white with dark cross streaks. Never very abundant.
Arion minimus.—The smallest Arion: not an inch long. Grey or yellowish. Feeds on fungi. Body wrinkled with microscopic spikes. Common. The young of A. ater might be mistaken for it.
Arion hortensis.—Grey with purple side bands. Foot-sole yellow. 1 to 1-1/2 inch in length. Generally found in gardens, as its name indicates.
Arion circumscriptus.—Very common in fields. A dark band down the back, foot-sole white. Very “sluggish.”