198 LAND AND FRESH-WATER M0LLTJ8KS. 
walk is slow; they swim very well, with the shell 
inverted, at the surface of the water, which, if 
shallow and not sufficient, is soon rendered 
glutinous with their mucus threads. 
The egg-masses are large, about two inches 
long, cylindrical, and slightly curved; the eggs are 
disposed in the capsules in two rows of about 
fifteen each, which are imbricated one on the 
other, but the length of the capsule, and conse¬ 
quently the number of eggs in each of them, are 
variable. 
It occurs in ditches and lakes on aquatic 
plants, and is abundant, though very local. It 
is remarkable for its periodical appearance in the 
same spots. It is recorded, from the neighbour¬ 
hood of Norwich on Siums; near Oxford; Dun- 
ster Castle, Somerset; Bala Lake, North Wales; 
and Windermere Lake; it ranges from Finland 
to the Pyrenees. 
Limma (Amphxfeplea) involuta —{the Involute 
Membrane Shell) (PL X., fig. 123).—It is easily 
distinguished from the last species by the sunken 
spire within the last whorl; the aperture of the 
shell is very large, and extends to the apex. 
The shell is small, polished, of a pale amber 
colour, extremely thin and membranous, as in 
L. glutinosa, with coarse longitudinal strim; its 
maximum length is five and a-half lines, and its 
greatest breadth three and a-half lines. 
