24 LYMN^CEA. 



p. 51 ; Planorhis lenticularis, Sturm, Fauna, VI, pi. 8, f. 16; 

 PlanorUs fontanus, Turton, Man., p. 110, f. 93; Planorhis 

 complanatus, Drapeinaud, Moll., p. 47, pi. 2, f. 20, 21, 22; 

 Rossmassler, Icon., II, p. 16, pi. 7, f. 116; Biard, p. I6l, pi. 6, 

 f. 4; Helix fontana, Lightfoot, Phil. Trans., LXXVI, pi. 2, f. 

 1 ; Montagu, Test. Brit., p. 462, pi. 6, f. 6 ; Maton and Racket, 

 Linn. Tr., VIII, p. 192; Brown, Wernerian Mem., II, p. 524; 

 Helix lenticularis, V. Alten., p. 35, pi. 2, f. 4. 



Shell pellucid, glossy, nearly destitute of wrinkles, reddish or 

 greyish horn-coloured ; lenticular, greatly flattened, almost 

 equally convex on both sides, and a little depressed in the 

 centre; with four volutions, the outer one subcarinate near the 

 middle, produced by the gradual outward slope of the shell, 

 both above and below ; a small central umbilicus on the under 

 side ; the internal angles of the ribs clasp the body nearly 

 equally on both sides, embracing nearly half the diameter of 

 the first volution ; margin very thin, and considerably oblique ; 

 aperture contracted, and almost brought to an angle externally. 

 Diameter not a quarter of an inch. 



Inhabits stagnant waters, usually adhering to aquatic plants. 



This shell may be easily confounded with the Segmentina 

 lineata, but is more compressed, and not so convex above, and 

 is destitute of the lines which mark the segments of that shell. 



Section IV. — Destitute of a carina; volutions rounded both 

 before and behind, and deeply umhilicated. 



10. Planorbis contrortus, pi. Ill, f. 30, 31. 



Planorhis contrortus, Miiller, Verm., II, p. 162; Draper- 

 naud, Moll., p. 42, pi. 1, f. 39, 40, 41 ; Sturm, Fauna, pi. 3, f. 

 4; Pfeiffer, p. 81, pi. 4, f. 11 ; Lamarck, An. San. Vert., VI, 

 pt. 2nd, p. 154 ; Brown, lUust. Conch., p. 33, pi. 14, f. 33, 34 ; 

 lb.. First Ed., pi. 41, f. 33, 34; Jeffreys, Linn. Tr., XVI, p. 

 383; Fleming, Brit. An., p. 277 ; Forbes, Mai. Mon., p. 13; 

 Rossmassler, Icon., II, p. 16, pi. 7, f. 117; Turton, Man., p. 

 113, f. 96; Brard, p. 157, pi. 6, f. 12, 13, 14; Alder, Mag. 

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

 Hist., VI, p. 51 ; Helix contorta, Linne, Syst. Nat., I, p. 1244; 

 Montagu, Test. Brit., p. 457, pi. 25, f. 6 ; Donovan, Brit. Sh., 

 Ill, pi. 99; Brown, Ency. Brit., 6th Ed., VI, p. 458; lb., 



