LYMN^CEA, 17 



convolving always on the same plane, and apparent on both 

 sides; aperture oblong, lunate, or subquadrate, its breadth being 

 nearly equal to its length, and sometimes greater ; outer lip 

 thickened, expanded, and its under part always extended for- 

 wards ; umbilicus very wide ; destitute of an operculum. 



Section I. — Volutions devoid of a carina, rounded on both 

 sides ; spire sliglitly concave. 



1. Planorbis corneus, pi. Ill, f. 21, 22, 23. 



Planorhis corneus, Drapernaud, p. 43, pi. 1, f. 42, 43, 44; 

 Pfeiffer, p. 77, pi. 4, f. 3, 4 ; Lamarck, An. San. Vert., VI, pt. 

 2nd, p. 152; Brard, p. 147, pi. 6, f. 1, 2; Brown, Illust. Conch., 

 p. 31, pi. 14, f. 31, 32, 33; lb.. First Ed., pi. 41, f. 31, 32, 33; 

 Jeffreys, Linn. Tr., XVI, p. 383 ; Fleming, Brit. An,, p. 277 ; 

 lb., Edin. Ency., VII, p. 69 ; Alder, Mag. Zool. and Bot., II, 

 p. 112; Thompson, Ann. and Mag. Nat. Hist., VI, p. 48; 

 Sowerby, Gen., f. 1; Turton, Man., p. 112, f. 95; Rossmassler, 

 Icon., II, p. 14, pi. 7, f. 113; Planorhis purpurens, Miiller, 

 Verm., II, p. 154; Planorhis similis, p. 166, young shell; Helix' 

 cornea, Donovan, Brit. Sh., II, pi. 39, f. 1 ; Montagu, Test. 

 Brit., p. 448 ; Brown, Wernerian Mem., p. 524 ; lb., Ency. 

 Brit., VI, p. 458; Heli.v nana. Pennant, Brit. Zcol., IV, p. 133, 

 pi. 83, f. 125, the young shell; p. 134, f. 126, the adult. 



Shell dextral, depressed ; spire consisting of four rapidly dimi- 

 nishing volutions, deeply divided by the suture, sunk below the 

 level of the outer, or body volution, and coiled upon its apex, 

 which gradually sinks, and forms a concavity, or umbilicus ; 

 under surface nearly flat, and exposing the whole volutions of 

 the spire ; entire body rounded on the sides ; the shell trans- 

 versely striated, and sometimes with some wrinkles, across the 

 volutions; aperture nearly equilateral, sublunated, and oblique; 

 outer lip thin ; inner lip reflected on the columella, forming a 

 continuous line with the peristome; colour, rufous or chestnut 

 above, pale yellowish-brown or bluish-grey beneath. Diameter 

 generally an inch, but often to be met with an inch and a 

 quarter. 



In the young condition, the volutions are provided with fine 

 spiral striaj. 



Found in slow rivers and stagnant ditches in England and 



D 



