56 
LAND AND FRESH-WATER MOLLUSKS. 
Paludina viviparct without food for three months., 
submitted them in their enfeebled state to a 
temperature of 23° F., and on dissolving their 
icy prisons he found them all living. He in a 
like manner experimented with Anodon cygneus 
with similar results. 
Paludina Listeri (PI. IV., fig. 27) differs from 
P. viviparct in its shell being thinner and shorter, 
the whorls more inflated or swollen, and the 
sutures consequently deeper, the mouth more 
circular, and the umbilicus more distinct. It 
is usually somewhat larger. 
This species is generally associated with the 
last, but is not of such frequent occurrence. 
The shells of this species collected from a 
pond on Hampstead Heath, London, have their 
apices eroded, which is due to the action of sul¬ 
phuretted hydrogen given off from the decom¬ 
posing animal and vegetable matters. 
The animal is very sluggish, and on being 
touched generally falls off the body upon which 
it may be crawling. The female in the autumn 
contains from twenty to thirty eggs, and the 
young are excluded at the end of two months. 
Genus Bithinia. 
Bithinia tentaculata —(the Teniacled Bithinia) 
(PI. III., fig. 14)—is a very common species on 
aquatic plants in streams, ditches, and canals 
