LAND AND FRESHWATER MOLLUSCA OF SUSSEX. 163 
Pisidium nitidum. The Glossy Pea-shell.—In ditches at Hen- 
field, Lewes and Eastbourne.—B. 
Fam. UNIONID. 
Unio pictorum. The Painter’s Mussel.—Generally distributed in 
ponds and streams. Common in the Cut near Lewes, and in the 
Ouse occasionally; varying very much in appearance, specimens in 
the Ouse being much darker, and having an extraneous coat, evi- 
dently from some matter with which the water is impregnated.—U. 
Mr. W. Jeffery reports its occurrence at Burton, near Petworth. 
It is somewhat singular that none of the Sussex lists include the 
allied species, Unio tumidus, which is very generally distributed 
throughout the country, and sometimes occurs in company with 
pictorum. In the parish of Harting neither of these two species 
has been met with. 
Anodonta cygnea. The Swan Musse].—Common in ponds and 
pools, in the mud of which it may be found deeply sunk, with the 
posterior end only of the shell, where the respiratory syphon is 
situated, above the surface. Some unusally large specimens of 
this mussel] have been taken out of the Vicarage Pond at Cowfold, 
near Horsham. One of these, now before me, measures seven 
inches by three inches and a half. This is much above the average 
size; but some years ago several were taken out of a decoy pond 
in Firle Park, Sussex, measuring eight inches in length and nine 
in circumference.* 
It would be proper to introduce here the family Dretssenide, in 
order to notice the Zebra Mussel, Dreitssena polymorpha, which 
is generally distributed in our navigable rivers; but none of the 
Sussex conchologists make mention of it in their lists, and for the 
present therefore it remains excluded from the freshwater Mollusca 
of that county. 
UNIVALVES (GASTEROPODA). 
Order PEcTINIBRANCHIATA.T 
Fam. NERITIDA. 
Neritina fluviatilis. The River Neritina.{—Usually found on 
a stony or gravelly bed in slow rivers, streams and lakes, into 
* Merrifield, ‘ Nat. Hist. Brighton,’ p. 155. 
+ Having comb-like gills. 
t Neritina is a diminutive of Nerita, the ancient name of a sea-shell, 
