16 LYMN^CEA. 



2. Physa acuta, pi. Ill, f. 9, 10. 



Physa acuta, J. Sowerby, MSS. ; Bulla funtinalis, Maton 

 and Racket, Linn. Tr., VIII, pi. 4, f. 1 ; Physa rivalis, Brown, 

 lUust. Conch., p. 30, pi. 14, f. 58, 59; lb., First Ed., pi. 41, f. 

 58, 59. 



Shell oblong-ovate, very thin, brittle, and transparent ; body 

 very large ; spire very short, consisting of four volutions, and 

 terminating in an acute apex; aperture oblong-ovate, somewhat 

 oblique, and lengthened beyond the body volution. Length 

 nearly half an inch ; breadth a quarter. 



Found in Anglesea, Wales, and first identified as British by 

 J. Sowerby, Esq., who bred it in a water-butt, and describes the 

 animal as differing materially from P.fontinalis. 



3. Physa hypnorum, pi. Ill, f. 17, 18. 



Physa hypnorum., Drapernaud, p. 55, pi. 3, f. 12, 13; 

 Lamarck, An. San. Vert., VI, pt. 2nd, p. 157 ; Pfelffer, p. 97» 

 pi. 4, f. 29; Brown, lUust. Conch., p. 30, pi. 14, f. 60, 61 ; lb., 

 First Ed., pi. 41, f. 60, 61 ; Alder, Mag. Zool. and Bot., II, p. 

 114; Turton, Man., p. 129, f. 113; Thompson, Ann. and Mag. 

 Nat. Hist., VI, p. 34 ; Jeffreys, Linn. Tr., XVII, p. 381 ; Bulla 

 hypnorum, Montagu, Test. Brit., p. 228 ; Brown, Wernerian 

 Mem., II, p. 517; lb., Ency. Brit., VI, p. 433; Maton and 

 Racket, Linn. Tr., VIII, p. 127, pi. 4, f. 3 ; Fleming, Edin. 

 Ency., VII, p. 85 ; Amplexa hypnorum, Fleming, Brit. An., p. 

 276; Limnea turrita, Sowerby, Gen., f. 10; Nauta hypnoriim, 

 Leach, Moll., p. 152; Planorhis turritus, Miiller, Verm., II, 

 p. 169. 



Shell sinistral, elongated, subcylindrical, very smooth, glossy, 

 and transparent, of a dark greenish horn colour ; body about 

 half the length of the shell ; spire consisting of four or five well 

 divided, and taper volutions, terminating in an acute apex; aper- 

 ture ovate, narrow, contracted above, and rounded beneath ; 

 pillar somewhat sinuated. 



Found in ditches, stagnant pools, and lakes in many places of 

 Great Britain and Ireland. 



Genus VIII.— PLANORBIS.— MUller. 



Shell discoidal, umbilicate; spire depressed; apex always dis- 

 tinct ; volutions heterostrophe, or revolving from right to left, 



