MALACOZOA. GASTEROPODA. PECTINIBEANCHIATA. 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. PalncUna 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 otlier turns ; the suture deeply impressed ; 

 the aperture roundish-ovate, the inner lij) nearly covering the 

 umbilicus. Length about an inch and afourtb, breadth nearly 

 an incli. 



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

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

 another hy Mr. Martin, at Torrie. 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. — Coclilea maxima, fusca 

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

 Cyclostoma viviparum. Drap. MolL Terr, et Fluv. 34. PL 1. f. 16, 

 17. — Paludina vivipara. Lamli. 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 v.diorls convex, rapidly enlarging, the last about 

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

 wutli the peristome complete, thin-edged, reiiexed on the 

 columella. Operculum somewhat calcareous, with con- 

 centric striae. 



