166 LAND AND FRESH-WATER MOLLUSKS. 
from the mouth, and may be seen in position by 
breaking off the outer part of the last whorl; it 
consists of a thin, spoon-shaped shelly plate 
attached to the folds of the columella by an elastic 
filament. When the animal comes out of the 
shell, the clausium is pushed against the colu¬ 
mella ; and the elasticity of its filament also 
admits of it closing the aperture on the snail 
withdrawing within the shell. The clausium is 
not secreted until the snail is about to complete 
its shell; and is not attached to the animal, but 
is merely an appendage to the mouth of the 
shell. 
About 300 species of Olausilce are known, the 
majority of which inhabit South-eastern Europe. 
Glausila is represented in the Upper Eocene of 
the Isle of Wight; and the four species at present 
living in England, also found fossilized in the 
newer Tertiary deposit of Essex, are as follows :—- 
Shell smooth, glossy.. ... C. laminata 
„ streaked, with raised lines. 
„ „ with two columella folds ... C.biplicata 
„ „ „ three „ „ ... C. rugosa 
„ „ „ four or five ; very fusiform C. Bolphii 
Clausilia biplicata— {the Folded Close Shell) 
(PI. IX., fig. 95)—is larger than any of its con¬ 
geners. The shell is two-thirds and occasionally 
three-fourths of an inch in length, with about 
