232 NOTES ON THE MOLLUSCA OF THE THAMES ESTUARY.
No doubt, owing to its extreme minuteness, and its habit of hiding
among moss, it is frequently overlooked.
II—Brackish Water Shells (generally classed as Marine) inhabiting
the Marshes of the Thames Estuary in Kent and Essex.
Order PECTINIBRANCHIATA.
Family LITTORINIDAE.
Littorina rudis, Maton. Small brackish water variety; asso-
ciated with Hydrobia ventrosa, and Assiminia grayana. Ditches
upon East Tilbury Marsh.
Hydrobia ulvae, Pennant. Grays, Tilbury, Greenhithe, and
Gravesend.
H. ventrosa, Montagu. From Erith to below Gravesend,
Kent ; Coldharbour Point to below Tilbury Fort, Essex.
H. similis, Draparnaud. Erith Marshes ; one dead shell at
Beckton ; two live and one dead shell, marshes near Abbey Wood,
1890.
Var. candida, Jeff. Occurs sparingly with type. (A clear
pellucid variety.)
H. jenkinsi, Smith. The most abundant shell of this genus
upon the Thames Marshes ; from the commencement of Plumstead
Marshes nearly to Northfleet, in Kent, and from Beckton to Cold-
harbour Point, Essex.
Var. ecarinata, Jenkins. Shell smooth, without keel or
tufts ; occurs with type.
Var. tumida, Jenkins. Shell much inflated, very short spire ;
ditch near Beckton.
Var. gracilis, Jenkins. Ditches; Rainham and Erith Marshes
Order PULMONOBRANCHIATA.
Family ASSIMINEDAE.
Assiminea grayana, Leach. Between Coldharbour Point
and Purfleet; also from Grays, extending some distance down the
river below Tilbury Fort ; and in Kent from Greenhithe to below
Gravesend; abounding in the canal near the latter place.
Family CARYCHIIDAE.
Melampus myosotis, Drap. Associated with Assiminea in
the same localities.