On the Land and Fresh-water Mollusca, &c, 89
The Colchester district is watered by three rivers, the
Colne and Blackwater wholly in Essex, and the Stour dividing
this county from Suffolk. Its boundaries are a line drawn
from Bures, through Coggeshall to Maldon, on the west side,
and on the east, south, and north the sea and rivers form its
confines.
The names and arrangement adopted in the paper are in
accordance with Mr. J. Gwyn Jeffreys' 'British Conchology.'2
Sphaeriidae.
Sphaerium corneum, Linn.—As is usually the case, this is
abundant in all the streams and ponds which are suitable.
I find it most variable, but I cannot satisfy myself that we
possess more than one of the varieties named by Jeffreys.
Var. flavescens occurs in the most rapid parts of a brook
two miles south of the town.
S. lacustre, Mull.—Occurs in many ponds, on gravel as
well as clay, and it is surprising how they manage to exist in
the stagnant and filthy water of some ponds.
Var. Brochoniana.—This form I find in the remains of the
moat of an old manor house at Birch, on Boulder Clay.
Pisidium amnicum, Mull.—Although usually so common, I
cannot say that I find it abundantly; perhaps I have not the
knack of searching for it.
P. fontinale, Drap.—In the marshes of the Colne, &c,
but not abundantly. I do not think we have any of the
named varieties, but I find the shell to be very variable.
P. pusillum, Gmelin.—Very abundant in shallow roadside
ditches which are dry for months at a time. This also is a
variable species, some specimens being nearly round, i.e.,
more ventricose than usual.
P. nitidum, Jen.—I do not find it abundant, but still the
river meadows generally seem to have some in most of the
ditches at one part or other. The long grasses growing in
2 'British Conchology, or an account of the Mollusca which now
inhabit the British Isles and the surrounding seas.' Vol. i. Land and
Fresh-water Shells. London, 1862.
L