THE NON-MARINE MOLLUSCS OF ESSEX.
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Class—PELECYPODA.
Order—EULAMELLIBRANCHIA.
Sub-order—SUBMYTILACEA.
Family—Dreissensiidae.
Genus—DREISSENSIA, Van Beneden, 1835
(emended by Fischer, 1886).
[Dreissensia polymorpha, Pallas.]
Family— Unionidae .
Genus— UNIO, Retzius, 1788.
[Unio littoralis, Lamark.] Extinct in Britain.
A.—Grays; (British Museum).
B.—*Clacton ; (British Museum).
Unio pictorum, Linne.
A.—River Stort; (Ingold) : Hatfield Forest ; (Hughes) ;
—41/2 inches long; (Christy) : River Roding ; Old
Mill" to Wanstead Park; (Crouch): Walthamstow;
(British Museum) ; Grays; Ilford; (K. and W.).
B.—River Chelmer, Felstead ; (French) : Coggeshall; (Laver,
saw specimens from here.—Turner) : Brook at Tilty ;
Dunmow; River Cann, Chignal; River Chelmer—very
green; (Christy): Broomfield; (E.N., vol. vii., p. 76).
Unio tumidus, Retz.
A.—Hatfield Forest ; (Ingold) : River Roding, Old Mill to
Wanstead Park ; (Crouch) : Ilford ; Walthamstow ;
(British Museum) : Docks; Grays; (British Museum).
[Unio margaritifer, Linne.]
Genus—ANODONTA, Lamark, 1799.
Anodonta cygnaea, Linne.
A.—River Stort—with form anatina ; (Ingold) : *01d River
Lea; (Cole) : Hatfield Forest (Hughes and E.N., vol.
iv., p. 223) : Wanstead Basin ; Eagle Pond, Snaresbrook ;
Walthamstow ; River Lea—anatina form ; River Roding,
Wanstead; (Crouch) : Ilford ; (K. and W.) : Lea
Valley ; (K. and W.) : Grays; (British Museum).