Vertigo (Sphyradium) edentula is dextral and without denticles. Perhaps the most common Vertigo. Partial to bracken.
Vertigo (Isthmia) minutissima.—Dextral and without denticles. Smaller, narrower, and more strongly striated than edentula, but rarer. All the Pupæ should be examined with a magnifier.
Balea perversa (i.e. sinistral) is a much larger shell belonging to the Clausilia family. Thin, dark horn-colour, semi-transparent, glossy, 7 to 8 whorls, local, but abundant where found. Chiefly found on trees.
Clausilia (Pirostoma) bidentata.—All our British clausilias are sinistral. The clausilium (little door) is an internal contrivance fastened to the pillar of the shell (whereas an operculum is attached to the body of a mollusc) by an elastic ligament to protect it against insect enemies when the animal withdraws. Bidentata has two denticles, fusiform and reddish-brown, as are all. Very common on walls and trees.
Clausilia (Pirostoma) rolphii.—Rare and local. Almost subterranean in habit. More coarsely striated than the last. The upper whorls nearly of the same breadth, forming a short cylinder.
Clausilia (Alinda) biplicata.—Very local. Chiefly on Thames willows. Larger than the two former, and streaked with white.
Clausilia (Marpessa) laminata.—Much like the former, but widely distributed. Usually found on beech and ash trees, and on limestone rocks. Smooth and glossy.
In the family Stenogyra we have three genera, Azeca, Cochlicopa, and Cæcilioides (with also the imported Stenogyra Goodallii, found only in pine-houses).
Stenogyra (Azeca) tridens is a small chrysalis-shaped, solid but semi-transparent shell, horn-coloured, with 3 denticles. Not rare in moist places.