92 On the Land and Fresh-water Mollusca
one may be found in the Colne. In a ditch running into this
river near Sheep-pen Bridge at times it is very plentiful; but
often for months this ditch is dried up, and then I do not
know where to find the snails.
P. fontinalis, Linn.—Frequent in all the brooks and
streams.
Limnaea peregra, Mull.—Everywhere.
Var. ovata.—I have never found this form except in the
Colne and Stour. Some specimens are very large and not
unlike L. auricularia.
Var. acuminata.—I find this also in the same localities as
the last.
Var. maritima.—Occurs in considerable numbers in the
brackish, almost salt, water of the ditches near Wyvenhoe
Park, in company with P. albus.
Var. scalariformis.—Frequent in the small drains of one
meadow near Birch Hall. There are all the intermediate
stages between the normal forms and those in which the
whorls of the shell are nearly separated.
L. Auricularia, Linn.—In the Stour and also in the Colne,
but the intermediate forms between L. peregra and this species
make it at times difficult to decide to which the varieties
belong.
L. stagnalis, Linn.—Frequent in the Stour, and especially
so in some years ; also in ponds in many parts of the district
where clay occurs. I never find it on gravel. In some
ponds at Wormingford the shells are quite two inches long.
L. palustris, Mull.—Frequent in ponds on all soils.
L. truncatula, Mull.-—Common everywhere. It is difficult
to understand how this snail exists in shallow roadside
puddles which are dry during months in the year. These
situations generally produce :—
Var. minor.—Commonly.
Var. major.—I have found this form in a pond near Bottle
End, Stanway, which is never dry, in company with L.
palustris.
L. glabra, Mull.—Ditches and shallow ponds, abundantly;
especially on gravelly soils. I once found it in a wet spot in