LYMN.ECEA. 23 



Found in ditches and other stagnant waters in Great Britain 

 and Ireland. 



8. Planorbis spirorbis, pi. Ill, f. 19, 20. 



Planorhis spirorbis, Miiller, Verm., II, p. 161 ; Brard, p. 

 156; Sturm, Fauna, pi. 45; Brown, Illust. Conch., p. 33, pi. 

 14, f. 42, 43; lb., First Ed., pi. 41, f. 44, 45; Turton, Man., 

 p. 115, f. 98 ; Alder, Mag. Zool. and Bot., II, p. 113 ; Forbes, 

 Mai. Mon., p. 13; Thompson, Ann. and Mag. Nat Hist., VI, 

 p. 50 ; Planorhis vortex, Drapernaud, Moll., p. 45, pi. 2, f. 6, 

 7 ; Jeffreys, Linn. Tr., XVI, p. 382 ; Pfeiffer, p. 79, pi- 4, f. 

 8 ; Helix spirorbis, Montagu, Test. Brit., Sup., p. 455, pi. 25, 

 f. 2; Maton and Racket, Linn. Tr., VIII, p. 191 ; Brown, Wer- 

 nerian Mem., II, p. 524; lb., Ency. Brit., 6th Ed., VI, p. 458; 

 Turton, Brit. Fauna, p. 187. 



Shell thin, semitransparent, brownish horn-colour, slightly 

 and equally concave both above and below ; with six gradually 

 increasing, rounded, nearly equal volutions, placed quite lateral 

 upon each other, the exterior one nearly round, provided with 

 a flattened carina; the whole shell covered with very fine trans- 

 versely oblique strise ; aperture subrotund, and rounded below. 

 Diameter about a quarter of an inch. 



Found in ditches and stagnant waters in Great Britain and 

 Ireland. 



This species seldom exceeds a quarter of an inch in diame- 

 ter, and may be distinguished from the P. vortex by its being 

 equally concave above and below, and in the keel on the mar- 

 gin of the outer volution being much less prominent, and, 

 indeed, in some specimens it is nearly obsolete ; when it is so, 

 the aperture is not at all angulated. It is, besides, not so thin 

 and depressed as the P. vortex, in proportion to its size. 



Section III. — Shell shining, translucent ; spire deeply mn- 

 bilicate ; volutions provided with a slight carina. 



9. Planorbis nitidus, pi. IV, f. 1, 2. 



Planorhis nitidus, Miiller, Verm., II, p. 263 ; Pfeiffer, p. 82, 

 pi. 4, f. 12, 13; Fleming, Brit. An., p. 278; Brown, Illust. 

 Conch,, p. 33, pi, 14, f. 48, 49; lb.. First Ed., pi. 41, f. 48, 

 49 ; Jeffreys, Linn. Tr., XVI, p. 389 ; Alder, Mag. Zool. and 

 Bot,, II, p. 114; Thompson, Ann. and Mag. Nat. Hist., VI, 



