Involute.] 



MOLLUSCA. 



27 



body, and two on the superior volutions ; surface with a few 

 obsolete wrinkles, or lines of growth ; aperture provided with a 

 thin, elastic, horny operculum. 



Found in the canal at Birmingham, where it has hitherto 

 been mistaken for the P. vivipara. 



This species may be distinguished from the P. vivipara by 

 the volutions being less inflated, in the suture being less deep, 

 the spire tapering less abruptly, and more obtuse at the apex ; 

 and in the whole shell being more cylindrical. 



3. Paludina impuba, pi. XIV, f. 72, 73 First Ed., pi. 



41, f. 72, 73. 



Paludina impura, Lamarck, 'An. San. Vert., VI, pt. 2nd, 

 p. 175; Brard, Coq. de Paris, p. 183, pi. 7, f. 2 ; Draper- 

 naud, Moll., p. 36, pi. 1, f. 19; Turton, Man., p. 134, f. 120; 

 Alder, Mag. Zool. and Bot., II, p. 116; Paludina tentaculata, 

 Fleming, Brit. An., p. 315 ; Thompson, Ann. and Mag. Nat. 

 Hist., VI, p. 17 ; Helix tentacidata, Donovan, Brit. Sh., Ill, 

 pi. 93 ; Pennant, Brit. Zool., IV, p. 140, pi. 86, f. 140; Mon- 

 tagu, Test. Brit., p. 389- 



Shell oblong-oval, thin, smooth, semitransparent ; spire con- 

 sisting of four or five ventricose volutions, deeply divided by 

 the suture, and terminating in an acute apex; aperture subor- 

 bicular, pointed above, and closed by a testaceous, concentrically 

 wrinkled, operculum, which is internally coated with a testaceous 

 covering, and its nucleus subcentral ; outer lip smooth on the 

 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. XIV, f. 74, 75 First Ed., 



pL41,f. 74, 75. 



Paludina ventricosa, Leach, MSS.; 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 ven- 

 tricosa, 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, ob- 

 lique, 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 35. — 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 distinguish the shells of this genus from those 

 of Littorina. 



I. Assiminia Grayana, pi. XVIII, f. 3, 4. 



Assiminia Grayana, Leach, MSS. ; Fleming, Brit. An., p. 

 275; Berkeley, Zool. Journ., V, p. 429, pi. 19, f . 4 ; Alder, 

 Mag. Zool. and Bot., II, p. 116; Nerita syncera hepatica, 

 Gray, Med. Repos., 1821, p. 239; Paludina Grayana, Potiez, 

 Gal., I, p. 251, pi. 25, f. 23, 24 ; Lymneus Grayanus, Jeffreys, 

 Linn. Trans., XVI, p. 378. 



Shell ovate, smooth, shining, dark reddish horn-colour, or 

 ferruginous ; body large ; spire small, consisting of three or 

 four abruptly tapering volutions, slightly divided by a nearly 

 transverse suture, and terminating in a somewhat acute apex ; 

 aperture ovate, slightly contracted at both extremities ; outer 

 lip thin, even ; inner lip smooth, a little reflected on the colu- 

 mella ; provided with an ovate, horny, blackish-brown opercu- 

 lum. Length a quarter of an inch ; breadth a little more than 

 half its length. 



Inhabits the Thames and other rivers, and small streams con- 

 nected with them, seldom beyond the point where the water is 

 brackish. 



Genus 36 Valvata Midler. 



Shell discoid, or conoid, with rounded, close-set, or depressed 

 volutions ; covered by an olive-coloured epidermis ; aperture 

 circular, not modified by the body ; peritreme acute, sharp- 

 edged, and continuous ; provided with a horny, orbicular oper- 

 culum, consisting of numerous gradually increasing volutions, 

 having an acute membraneous margin, which forms a spiral 

 elevation on the external surface. 



1. Valvata piscinalis, pi. XIV, f. 62, 63 — First Ed., pi. 

 41, f. 62, 63. 



Valvata piscinalis, Lamarck, An. San. Vert., VI, pt. 2nd, p. 

 172; Alder, Mag. Zool. and Bot., II, p. 116; Kenyon, Mag. 

 Nat. Hist., Ill, p. 425, f. b, c, d; Fleming, Brit. An., p. 286 ; 

 Forbes, Mai. Mon., p. 20 ; Thompson, Ann. and Mag. Nat. 

 Hist., VI, p. 17; Valvata depressa, Pfeiffer, Syst., p. 100, pi. 

 4, f. 33; Valvata obtusa, Turton, Man., p. 130, f. 114; Brard, 

 Coq. de Paris, p. 190, pi. 6, f. 17; Cyclostoma obtusion, Dra- 

 pernaud, p. 33, pi. 1, f. 14; Turbo fontinalis, Montagu, Test. 

 Brit., p. 348, pi. 22, f. 4 ; Lymnea fontinalis, Fleming, Edin. 

 Ency., VII, p. 78 ; Turbo thermalis, Dillwyn, p. 852. 



Shell thin, subpellucid, horn-coloured, smooth, with fine spiral 

 stria? throughout, and a few obscure, concentric lines of growth ; 

 length and breadth nearly equal; body very large, much inflated, 

 with a deep central umbilicus at its base ; spire small, short, 

 consisting of four tumid, deeply defined volutions ; aperture 

 orbicular; peristome thin, the inner lip slightly attached to the 

 body volution. Length little more than a quarter of an inch. 



Common in rivers, canals, ponds, and lakes in Britain, and in 

 ditches in the Curraghs, Isle of Man. 



Fig. 64, 65, pi. XIV, is a permanent variety, with the spire 

 more produced, and the volutions somewhat scalariform ; found 

 at Clonoony, King's County, Ireland. 



