CLAUSILIA. 105 
Var. I. viridula (Jeff). Transparent greenish white. 
Var. II. stmplex (Mog). Without denticle. 
Genus.—CLausiLia Draparnaud. 
Shell fusiform, British species all sinistral; furnished with a c/azs- 
zlium ; mouth denticulated. 
This genus derives its name from a peculiar character- 
istic—a little door (Lat. claustlium). 
This interesting provision of nature against the attacks 
of such enemies as beetles, &c., differs from an operculum 
thus:—It is not fastened to the anzma/, but to the pillar 
of the she/Z by an elastic filament. When the animal is 
within the shell this contractile filament draws the c/azs- 
tlium close over the aperture, about half a turn from the 
entrance, and when the animal emerges it pushes aside 
the little “spring door,” which then lies flat against the 
columella. 
Sub-genus.—PIROSTOMA Vest. 
I. C. BIDENTATA (wth 2 teeth) Strom. Pi. V., f. 1. 
[=C. ruGosa (wrinkled), Draparnaiud.) 
Fusiform, purplish brown, but varying in colour; marked with small 
streaks of white; closely and irregularly striated in the line of growth; 
whorls 1O—13; sfere tapering toa blunt point; *ozth pear-shaped, 
expanding like a funnel, angulated above ; f/¢catzons, 2 on pillar, with 
2 or 3 ribs between them, a plication behind pillar lip, near which is a 
spiral fold; 1 or 2 teeth inside over Lip ; wmbilicus narrow ; clauselium 
shaped much like a ‘ shoehorn.’ A. 11—1I3 mm. B. 3 mm. 
This common shell is distributed throughout the whole 
of the British Isles, and is found on walls, the rough bark 
