THE POUCH-SHELL. 
337 
the muzzle. In one respect, the Ampullaria seems to be a connecting link between the gill- 
bearing and lung-bearing mollusks, being said by high authorities to possess a pulmonic or 
lung sac, in addition to its gills. 
POND-SNAIL . — Limncea stagnalis. (Natural size.) 
In the accompanying illustration the common Pond-snail, or Limncea, is shown in the 
act of climbing up the stem of a water-plant. In all the members of this family the shell is 
thin, and sufficiently capacious to con- 
tain the entire animal when it desires 
to withdraw itself into its home. The 
aperture is simply rounded, without 
notches or ridges, and the lip is sharp. 
In the water-glass of the illustra- 
tion will be observed the pond-snail, an 
equally common European shell, called 
from its flattened whorls the Planorbis. 
In this animal, the foot is short and 
round ; the tentacles are long, slender, 
and leave the edges at their inner bases. 
Both this and the preceding species are 
in the habit of burying themselves in 
the mud during a drought, and there 
passing a semi-torpid existence. 
A very remarkable species, called, 
from its peculiar shape, the Fresh- 
water or Eiyer Limpet ( Ancylus la- 
custris ), is found in various parts of 
America, Madeira, and some portions of 
Europe. It inhabits swiftly running 
streams, and is mostly seen attached to 
stony and aquatic plants. Although 
the shell is so limpet-like, the animal 
does not partake of the resemblance, 
being very like that of the pond -snail, 
and having triangular tentacles with the 
eyes at their bases. The generic term, 
Ancylus , is of Greek origin, and signi- 
fies a small round shield or target. 
The little elongated Pouch-shell, a species of a rather small genus, extending over the 
greater part of the globe, is thin, spiral, polished, and the aperture is rounded in front. In 
Vol. m.-43. 
P T, A N ORTH S . — Planorbis corneus. (Natural size.) 
