6 PERISTOMIDA. 



1. AssiMiNiA Grayana, pi. I, f. 12, 13. 



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; Brown, lUust. Conch., p. 27, 

 pi. 1 8, f. .3, 4 ; Nerita syncera hepatica, Gray, Med. Rep., 

 1821, p. 239; Paludina Grayana, Potiez, Gal., I, p. 251, 

 pi. 25, f. 23, 24 ; Lymneus Grayaniis, 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 IV.— VALVATA— Muller. 



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. 



\. VaLVATA PISCINALIS, pi. I, f. 14, 15. 



Valvata pisdnalis, 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; Brown, Illust. Conch., p. 27, pi. 14, f. 62, 63, 

 64, 65; Valvata depressa, Pfeiffer, Syst., p. 100, pi. 4, f. 33; 

 Valvata ohtusa, Turton, Man., p. 130, f. 114; Brard, Coq. do 

 Paris, p. 190, pi. 6, f. 17; Cydustoma ohfnsmn, Drapcrnaud, p. 



