198 LAND AND: FRESH-WATER MOLLUSKS. 
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 shghtly curved ; the eggs are 
disposed in the capsules m 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 vadatles 
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 Stwms; near Oxford; Dun- 
ster Castle, Somerset; Bala Lake, North Wales ; 
and Windermere Lake; it ranges from Finland 
to the Pyrenees. 
Limn#A (AMPHIPEPLEA) 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 striz; its 
maximum length is five and a-half lines, and its 
greatest breadth three and a-half lines. 
