206 ON THE LAND AND FRESH-WATER MOLLUSCA
Note.—In the following list I have inserted (in brackets, but have
not included in the above synopsis, being outside the boundary)
one species from the chalk at Grays Thurrock, Helix caperata. In
this locality, and also at Purfleet, I have long expected to find the
operculated snail, Cyclostoma elegans, which is so common in hedge-
banks on the Kentish side of the Thames ; but have hitherto been
unable to find even a dead shell. It occurs, however, as a fossil in
various parts of the county ; and as such is included in the Felstead
list. 3
Class PELECYPODA (Bivalve Shells) ;
Order LAMELLIBRANCHIATA;
Family SPHAERIIDAE.
Sphaerium corneum, L. Grips and ponds—Barking Side,
Wanstead, Leytonstone, Whips Cross, Walthamstow, Eastham ;
abundant.
Pisidium amnicum, Muller. Pond at Fern Hall, Barking
Side, and Wanstead Basin ; not common.
Pisidium pusillum, Gmelin. Pond at Fern Hall; common.
This pond has of late years been partially filled up and will soon
cease to exist.
Family UNIONIDAE.
Unio tumidus, Philippsson. River Roding, Old Mill to
Wanstead Park; fairly abundant, but not of great size.
Unio pictorum, L. Ditto, ditto.
Anodonta cygnaea, L. Wanstead Basin, Eagle Pond, Snares-
brook (51/4 in.), Walthamstow, River Lea; common.
Anodonta anatina, L. River Roding, Wanstead ; abundant,
but always of small size.
Class GASTROPODA, (Univalve Shells.)
Order PECTINIBRANCHIATA.
Family NERITIDAE.
Neritina fluviatilis, L. River Roding, Crooked Meadow,
St. Swithin's, to Wanstead Park ; abundant. In River Lea, Temple
Mills, a few only alive, but dead shells are common, and are always
more conspicuous, as the epidermis soon erodes.
Live specimens of C. elegans have since been found in a limited area at Felstead (vide
E. N., vol. iv. pp. 92-94).