ALLUVIUM AT WALTHAMSTOW, ESSEX.
17
Planorbis contortus (Linn.) Anodonta cygnea (Linn.)
,, fontanus (Lightft.) Sphaerium corneum (Linn.)
Physa fontinalis (Linn.) Pisidium amnicum (Linn.)
,, hypnorum (Linn.)
Bithynia tentaculata (Linn.)
„ leachii (Shepp.)
Vivipara vivipara (Linn.)
Valvata piscinalis (Mull.)
,, cristata, Mull.
Neritina fluviatilis (Linn.)
Unio tumidus, Retz.
,, supinum, A. Schm.
,, henslowianum (Shepp.)
„ subtruncatum, Malm.
„ pulchellum, Jenyns.
„ pusillum (Gmel.)
„ nitidum, Jenyns.
,, obtusale, Pfr.
„ milium, Held.
The following species, previously recorded from these beds,
we did not find :—
Acanthinula lamellata (Jeff.) Vivipara contecta (Millet)
Helicella caperata (Mont.) Unio pictorum (Linn.)
NOTES ON THE SPECIES.
Arion ater (Linn). Several calcareous granules representing
the internal shell of this species were found. It has not hitherto
been detected in these, or in any other Holocene deposit in
Essex, though it is known from the Pleistocene of Ilford.
Of the ten species of Vitrea living in this country, all but
three were met with, the exceptions being V. pura and "glabra"
and V. excavata. V. alliaria is represented by a single example,
and is of considerable interest, since it has hitherto been only
known fossil in these islands from the Pleistocene of Ightham
and Happaway Cavern. V. nitidula was very common and is
separable into two forms, a larger one attaining a maximum
diameter of 11 mm., and a smaller one of only 6.5 mm. The
latter is known on the Continent under the name of V. nitens
(Mich).
Agriolimax agrestis (Linn) was represented by eight
examples. Only a single specimen has hitherto been obtained
from these beds.
Punctum pygmaeum (Drap) has not previously been
recorded from the Lea alluvium and now but a solitary example
establishes its presence.
Hygromia granulata (Alder) is another new record for
these beds; but, although several specimens were found, all are
immature.