64 LAND AND FRESH-WATER SHELLS. 



Family I. 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. fluviatilis. 12 



Family II. Paludinidse. 



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 i-fths inch. Ponds, lakes, canals, 

 and slow rivers. P. vivipara^ 



(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 i-fths 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 



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

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

 dark bands. 



13 v. albida, white ; v. unicolor, bandless ; v. atro-purpura> black, which 

 when viewed by transmitted light is purple. 



14 v. vir&scens, greenish, unicolor. 



