MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 123 



Shell ovato-conical or subglobose, spiral, covered with 

 a thin epidermis ; the turns convex, rapidly enlarging, 

 the last ventricose ; the aperture roundish-oval, angular 

 behind, with the peristome complete, thin-edged, reflexed 

 on the columella. Operculum thin and horny, with 

 concentric striae. 



1. Paludina vivipara. Viviparous Marsh-Shell. 



Shell thin, ovato-conical, with the apex pointed, the turns 

 five, thin, very convex, transversely striated; the last turn 

 very large, olivaceous with three brown bands, two of which 

 are apparent on the other turns ; the suture deeply impressed ; 

 the aperture roundish-ovate, the inner lip nearly covering the 

 umbilicus. Length about an inch and a fourth, breadth nearly 

 an inch. 



A dead shell was found on the beach near the mouth of the 

 Dee, in the spring of 1842, by Mr. Alexander Cruickshank; 

 another by Mr. Martin, at Tome. The species has not been 

 found alive in the district. Its occurrence on our coasts in- 

 dicates the source whence probably are derived the shells of 

 Bythinia tentaculata, Littorina muriatica, and Neritrina flu- 

 viatilis, sometimes cast on the beaches. 



Helix vivipara. Linn. Fauna. Suec. 529. Cochlea maxima, fusca 

 give nigricans, fasciata. Lister, Anim. Angl. 133. PI. 2. f. 18. 

 Cyclostoma viviparum. Drap. MolL Terr, et Fluv. 34. PI. 1. f. J6, 

 17. Paludina vivipara. Lamk.Syst.vi. 173. Paludina vivipara. 

 Flem. Brit. Anim. Paludina vivipara. Gray's Turton, 90. PI. 18. 

 f. 118. 



GENUS 2. BYTHINIA. 



Animal elongated, spiral ; with theheadproboscidiform ; 

 two contractile, tapering, setaceous tentacula, bearing the 

 eyes on prominences at their base externally ; the mouth 

 with a small hispid lingual mass ; the foot oval, with 

 a marginal groove at the anterior part. 



Shell ovato-conical, spiral, covered with a thin epider- 

 mis ; the whorls convex, rapidly enlarging, the last about 

 as long as the spire ; the aperture oval, angular behind, 

 with the peristome complete, thin-edged, reflexed on the 

 columella. Operculum somewhat calcareous, with con- 

 centric striae. 



