PERISTOMIDA. 5 



edge, moderately strong, with a slightly raised internal rib ; 

 inner lip a little reflected on the columella; external surface 

 smooth, and of a yellowish horn colour. Length half an inch ; 

 diameter three-eighths. 



This is a very common shell, inhabiting most slow rivers, 

 streams, and stagnant waters. 



Drapernaud, pi. 1, f. 20, figures a variety of this species 

 which is less, shorter, and more conical. 



4. Paludina ventricosa, pi. I, f. 10, 11. 



Paludina ventricosa, Leach, MSS.; Brown, Illust. Conch., p. 

 27, pi. 14, f. 74, 75 ; Paludina acuta, Fleming, Brit. An., p. 

 315; Paludina similis, Turton, Man., p. 135, f. 121 ; Alder, 

 Mag. Zool. and Bot., II, p. 116; Turbo Leachii, Sheppard, 

 Linn. Trans., XIV, p. 152; Cyclostoma simile, Drapernaud, 

 Hist, des Moll., p. 31, pi. 4, f. 15? Bithinia ventricosa, Gray, 

 Med. Rep., 1821, p. 239- 



Shell oblong-ovate, conic, smooth, semitransparent, of a yel- 

 lowish horn colour; body large, tumid; spire abruptly tapering, 

 and consisting of four much inflated volutions, deeply divided 

 by the suture, and terminating in a sharp apex ; aperture 

 nearly orbicular, somewhat outwardly produced ; outer lip 

 sharp-edged ; pillar lip slightly reflected on the columella, with 

 a small, oblique, subumbilicus behind ; aperture protected by a 

 testaceous operculum. Length a quarter of an inch ; breadth 

 two lines. 



In some specimens the body volution is slightly decussated, 

 the spiral striae being somewhat more obvious than the longi- 

 tudinal. 



Found in ditches at Battersea, near the Thames ; and other 

 places in the south of England. 



Genus III— ASSIMINIA— Leach. 



Shell somewhat oval, light, solid, covered with a horny epi- 

 dermis; spire produced into an acute pyramid; volutions slightly 

 angulated in the centre, rounded beneath; aperture elliptical, 

 somewhat modified by the body volution; inner lip plain; colu- 

 mella imperforate ; outer lip thin. 



It is difficult to dis«)inguish the shells of this genus from those 

 of Littorina, 



