64 LAND AND FRESH-WATER SHELLS. 



Family L — Neritidae. 



Shell semiglobose ; spire small, flat, excentric, mouth semi- 

 circular ; operculum shelly, with a plate-like appendage on its 

 under side. 



1. Neritina. 



{a) Shell ovate, solid, glossy, yellowish or brownish, with white 

 purple, brown or pink chequerings ; spire short, lateral, composed 

 of three whorls, the last one being excessively disproportionate ; 

 mouth semilunar; operculum semilunar, yellowish, bordered with 

 orange, and with a strong, raised, grooved spire placed at one end 

 of its lower surface. Length 3 lines. In canals and rivers with 

 stony bottoms. N. fliwiatilis}''^ 



Family II. — Paludinidae. 



Shell cone-shaped, ventricose ; mouth oval ; operculum con- 

 centrically striated. Body oval ; eyes sessile or placed on 

 pedicels at the base of the tentacles ; gills internal. 



2. Paludina. — Animal ovoviviparous ; eyes placed on pedicels ; 

 operculum horny. 



{a) Shell conically oval, ventricose, dull yellowish-green with 

 three brown bands on the body whorl, and two upon each of the 

 preceding whorls ; umbilicus none or represented by a slit ; mouth 

 an irregular oval. Length i to ifths inch. Ponds, lakes, canals, 

 and slow rivers. P. viviparaP 



(b) Shell conoid, very ventricose, brown olive marked with 

 three brownish bands on the body whorl, and with two on the 

 preceding whorls ; spire blunt or sharp : sutures very deep ; 

 umbilicus distinct, narrow, deep ; mouth nearly circular. Length 

 I to ifths inch. Canals and stagnant waters. P. contecta}'^ 



3. Bythinia. — Animal oviparous ; operculum shelly. 



{a) Shell ovoid, somewhat conical, glossy, thin, solid, yellowish- 

 horn colour, semi-transparent ; whorls six, convex, the body-whorl 



'- V. cerina, straw-yellow, unicolor ; v. nigrescens, black or blackish ; v. 

 imdulata, with some transverse dark bands ; v. trifasciata., with three spiral 

 dark bands. 



'^ V. albida, white ; v. unicolor, bandless ; v. atro-piirpitra, black, which 

 when viewed by transmitted light is purple. 



" V. virescens, greenish, unicolor. 



