NERITINA. ye 
Crass II.—GASTEROPODA (belly forming the foot) or 
UNIVALVES. 
Order IT—PECTINIBRANCHIATA. 
Family I—NERITID&. 
Genus.— NERITINA. 
N. FLUVIATILIS (inhabiting rivers). 
Ovate, solid, glossy, chequered brown and white and 
purple; whorls three; spire short; operculum semi-lunar. 
This prettily marked shell is found in many parts of 
Great Britain attached to stones in running water and 
canals. It is the most solid of the freshwater shells, 
and reminds us of its marine cousins, the Littorine, so 
common on seaweed. 
i 
Family I[.—PALUDINID& (living in marshes). 
Genus I.—PALUDINA. 
1. P. cont&cra (covered by operculum). 
Conical, diaphanous, fairly glossy, light green, with 
darker bands of the same colour; whorls seven, very 
convex; sutwre very deep; mouth almost circular, but 
angulated above; wmbilicus small, but deep and distinct; 
operculum thin. 
