WATER SNAILS. 
193 
Now this snail is a favourite food of ducks and 
geese, and the proximity of a farm, where these 
birds were kept, to the pond with L. stagnalis 
suggests to me the probable cause of their 
disappearance; but the eggs having escaped 
the general despoliation remained to replace 
their predecessors, and after the end of the 
first year attained to the adult condition. I had 
no opportunities of determining whether in the 
interval the pond was unfrequented by the geese, 
which appears somewhat necessary to account 
for the preservation of the young snails until 
they arrived at maturity. 
In other districts, to call in the aid of the 
wild ducks and herons, which prey upon them, 
as the agents of extermination, is quite fea¬ 
sible. 
Limnjia palustrts —(the Marsh Mud Shell) 
(PL X., fig. 113).—The shell of this species is 
oblong, conical, and pointed; colour, yellow to 
brown; whorls, six to seven, rounded, slightly 
convex, with a rather deep suture; the last whorl 
is large; the aperture is nearly half the length of 
the shell, purplish and glossy in the inside; the 
inner lip expanded, and partially covering the 
slight umbilicus; the maximum length is about 
three-fourths of an inch, but variable in size, as 
also in colour and form. Shells occur with spiral 
narrow white bands. Not unfrequently the spire 
o 
