38 THE ESSEX NATURALIST
Creek. Egg capsules and the veliger larvae are common in tho
plankton in spring and early summer.
Littorina saxatilis (Olivi) Rough Winkle
Very common on the shore, from Maldon seawards in the
Blackwater and in the Colne estuary. There is a wide range of
habitat and some different varieties of the species are associated
with these.
Littorina littoralis (Linne) Flat Winkle
Fairly common seawards of Osea Island under fucoid weeds
at the base of sea walls and sometimes among shells and stones
lower on the shore.
Hydrobiidae
Hydrobia ventrosa (Montagu)
Shells collected from the litter in saltings at East Mersea
(1962). The species is normally associated with estuarine con-
ditions and may be common in the brackish water regions of the
Blackwater and Colne.
Hydrobia jenkinsi Smith
Mostly a freshwater species but is also found in brackish water.
It is common in nearly all the drainage dykes around the Black-
water and may also be found where freshwater runs onto the
shore or into saltings. Both the keeled and normal shell forms
occur.
Hydrobia ulvae Pennant
Very common on the upper and middle shore and in saltings
throughout the tidal regions of the Blackwater from Maldon sea-
wards. Found in Saltmarsh pools and among roots of plants, on
the surface of mud and sand, and under shells and stones.
Acmea subcylindrica (Linne)
Only one record from the Blackwater; a shell collected from
the litter along the seawall in Bradwell Creek.
Rissoidae
Cingula semicostata (Montagu)
Shells only; common on the shell bank, St. Peter's Flats.
Rissoa membranacea (J. Adams)
Shells very common on beaches and in the litter at high water
mark. No living specimens collected.
Assimineidae
Assiminea grayana Fleming
A common species, under stones, wood and litter along high
water mark in saltings. Extends from the Phragmites beds of the
Blackwater above Maldon bridge to the saltings of East Mersea
and Colne Point.