86 PULMONIFERA.—LIMNEAD&, 
of the fluid necessary for their respiration and 
lige. 
GENUS LIMNEUS. 
In this genus the shell is ovate, oblong, or tur- 
reted, thin and horny, and transparent. The aperture 
is ovate or expanded, the margin entire, and the 
pillar marked with a single oblique plait running 
into the axis.. The animal has a short broad foot; the 
head and snout, and the ten- 
tacles, are also all charac- 
terised by peculiar breadth ; 
the two eyes are placed in 
front of the base of the last- 
named organs. ‘he mantle 
has an even edge sometimes 
reflected upon the shell, but 
never covering it. The tongue 
is armed with many trans- 
verse rows of short, hooked 
teeth. : 
The largest British species 
is the Lake Mud Shell (Zim- 
neus stagnalis), which attains 
a length of two inches, and a 
diameter of one. In the 
ah See large rivers of Kastern Europe 
it grows to a much larger 
size. The shell is thin and brittle, of a greyish 
hue, often covered with an extraneous coat; the 
spire is composed of about seven whorls, tapering 
toa fine point ; the last whorl is striated lengthwise, 
* Gray’s Land and Fresh-water Shells, 229. 
