THE NON-MARINE MOLLUSCA OF MERSEA ISLAND 361
Figure 3.—a, Leucophytia bidentata; b and c, Phytia myosotis, two common
shell forms.
Leucophytia bidentata (Montagu). Occasionally found in the
saltings, among the roots of halophytes, particularly at
West Mersea. The small white shells of this species are
commonly found in the litter at high water mark. A
typical shell form is shown in Fig. 3 a.
Phytia myosotis (Draparnaud). Very common in all saltings,
among the roots of halophytes and under stones and litter.
Shells are abundant in the litter. Some shell variations
occur; there usually being two folds, with perhaps one or
even two small denticles posterior to them, on the colu-
mellar and sometimes one or more denticles on the inside
of the lip. Living specimens frequently have a line of fine
projections from the periostracum beneath the suture, and
in many cases this is almost as well developed as to resemble
the keel of Potamopyrgus. Some of these features are
shown in Fig. 3 b and c.
Family Lymnaeidae
Galba truncatula (Muller). Occasionally found living in ditches
along the landward edges of the drained marshes and as
shells on higher parts of the island. This species is
amphibious and has been shown to be tolerant to long dry
spells.
Radix peregra (Muller). Common in freshwater of marsh fleets
and ditches and in a few ponds on higher ground.
Family Planorbidae
Anisus leucostoma Millet. Recorded at one pond, near Barrow
Hill, in association with Radix peregra. This species is
commonly found in ponds which tend to dry up in summer.
Gyraulus crista (L.). Abundant among Lemna sp. and other
weeds in wet ditches along the landward edge of the
drained marshes, particularly at West Mersea.