46
THE ESSEX NATURALIST
number recorded from grab sampling, 25/m3, was obtained at
station TL.3 (6.12.1961).
Cardium edule Linne Common Cockle
Very common on the tidal flats of the Blackwater in sand and
sandy-mud, from middle shore to just below low water mark.
Extends from the low salinity areas below Maldon to the offshore
sand banks. Sampling on the north shore of the Blackwater
produced, in 1964, up to 416 per m3. The sub-species, lamarcki
Reeve, probably occurs locally in saltings or other areas of wide
salinity fluctuation. Some living specimens of this sub-species
were collected from a tank connected to the cooling system of
Bradwell Power Station in 1963. The animals must have entered
as planktonic larvae.
Cardium crassum Gmelin
Only one record; a single valve in poor condition, collected in
a dredge sample from the middle of the Blackwater in October
1960.
Veneridae
Venerupis aurea (Gmelin)
Shells are common on most shores of the Blackwater and Colne
estuaries. Living specimens have been obtained from Thirslet
Creek in 1960 and 1962. The species was previously recorded in
1888 (Cole) and "... obtained alive from the mud of Mersea, being
fairly abundant", by Sorby (1903).
Venerupis pullastra (Montagu)
Shells are common on the shores of the Blackwater, and some
living specimens were taken on the lower shore of Mersea Island
in 1964.
Venerupis decussata fusca (Gmelin)
Single valves occasionally found on the shores or taken in
dredge samples, but no living specimens found.
Petricolidae
Petricola pholadiformis Lamarck
Introduced from North America with imported oysters in the
1880's. First recorded by H. C. Sorby in 1901. Common and
widespread, burrowing into mud on the lower shore and below
low water mark in the Blackwater. Shells commonly washed up
on the shore.
Tellinidae
Tellina tenuis da Costa
Not common. Shells only, dredged from sandy bottoms at
the mouth of the Blackwater and in Whitaker Channel (4.6.1965).
Tellina fabula Gmelin
Not common. Shells found with those of T. tenuis.