90 On the Land and Fresh-water Mollusca
the water beside the drinking-places for cattle I find most
productive.
I consider this to be a most unsatisfactory family, and
question very much whether it will not be necessary to reduce
the number of species to three, and call the others varieties.
Unionidae .
Unio pictorum, Linn.—I have seen shells of this species
from the river at Coggeshall, but I have never taken it
myself. They were the ordinary form, and I do not think
it occurs elsewhere within my boundaries.
Anodonta cygnea, Linn.—In every stream and many
ponds.
Var. radiata.—In almost stagnant ponds; at Bromley
Lodge very large specimens occur, but I think the shells are
thinner than in the normal form.
A. anatina, Linn., appears to me to be only a variety of
the above. The intermediate forms are many, and I think
it is only a question of food. I have stocked a suitable pond
with anatina, and hope one day to note the result.
Neritidae.
Neritina fluviatilis, Linn.—Plentifully on stones in all
our streams. The markings are very varied.
PALUDINIDAE.
Paludina contecta, Millet.—In the Stour the specimens
are very large, but I do not find it to be an inhabitant of any
other stream.
Bythinia tentaculata, Linn.—Very frequent in both run-
ning and still waters. The most abundant fossil at Copford.
B. Leachii, Shepp.—Occurs in the same habitats as the
last species, but is much less abundant.
Valvatidae.
Valvata piscinalis, Mull.—Frequent in all our streams,
and in the fossil state at Copford in great plenty.