INVOLUTE. | 
p- 85; Amplexa hypnorum, Fleming, Brit. An., p- 276; Lim- 
nea turrita, Sowerby, Genera, f. 10; Nauta hypnorwn, Leach, 
Moll., p. 152; Planorbis 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 40.—P.Lanorsis.—Miiller. 
Shell discoidal, umbilicate; spire depressed; apex always dis- 
tinct; volutions heterostrophe, or revolving from right to left, 
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 slightly concave. 
1. PLANoRBIS coRNEUS, pl. XIV, f.31, 32, 33.—First Ed., 
pl. 41, f. 31, 32, 33. 
Planorbis corneus, Drapernaud, p. 43, pl. 1, f. 42, 43, 44; 
Pfeiffer, p. 77, pl. 4, f. 3, 4; Lamarck, An. San. Vert., VI, pt. 
2nd, p. 152; Brard, p. 147, pl. 6, f. 1, 2; Jeffreys, Linn. Tr., 
XVI, p. 383; Fleming, Brit. An., p. 277; Ib., Edin. Ency., 
VII, p.69; Alder, Mag. Zool. and Bot., II, p. 112; Thompson, 
Ann. and Mag. Nat. Hist., VI, p. 34; Sowerby, Genera, f. 1; 
Turton, Man., p. 112, f.95; Rossmassler, Icon., II, p. 14, pl. 
7, f. 113; Planorbis purpureus, Miiller, Verm., II, p. 154; 
Planorbis similis, p. 166, young shell; Helia cornea, Donovan, 
Brit. Sh., II, pl. 39, f. 1; Montagu, Test. Brit., p. 448; Brown, 
Wernerian Mem., p. 524; Ib., Ency. Brit. VI, p. 458; Helix 
nana, Pennant, Brit. Zool., IV, p. 133, pl. 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 yolutions are provided with fine 
spiral striae. 
Found in slow riyerg and stagnant ditches in England and 
Treland. 
2. PLANoRBis ALBus, pl. XIV, f. 52, 53.—First Ed., pl. 41, 
£262.53. 
Planorbis albus, Miiller, Verm., II, p. 164; Pfeiffer, p. 80, 
MOLLUSCA. 31 
pl. 4, f. 9, 10; Leach, Moll., p. 156; Jeffreys, Linn. Tr., XVI, 
p- 387; Fleming, Edin. Ency., VII, p. 69; Ib., Brit. An.,_p. 
278; Turton, Man., p. 114, f.97; Alder, Mag. Zool. and Bot., 
IJ, p. 113; Forbes, Mal. Mon., p. 13; Thompson, Ann. and 
Mag. Nat. Hist., VI, p. 48; Planorbis hispidus, Drapernaud, 
p. 43, pl. 1, £.45, 46, 47, 48; Lamarck, An. San. Vert., VI, pt. 
2nd, p. 154; Brard, p. 159, pl. 6, f. 6, 7; Helix alba, Montagu, 
Test. Brit., p. 459, pl. 25, f.7; Brown, Wernerian Mem., II, p. 
524; Ib., Ency. Brit., VI, p. 458. 
Variety 1. Shell smooth, shining, and white. 
Planorbis glaber, Jeffreys, Linn. Tr., XVI, p. 337. 
Shell dextral, thin, pale yellowish-white, subpellucid, depres- 
sed; body yolution very large, rounded on the sides; spire 
consisting of four rapidly decreasing volutions, which are equally 
conyex both above and below; the apex of the spire somewhat 
sunk, forming a subumbilicus, and the under surface more 
concave; whole external surface covered with fine, elevated, 
close-set, transverse, and spiral strie, producing a reticulated 
appearance, which are provided with dicidous bristles; aperture 
very large, sublunate, somewhat higher than wide, clasping the 
body volution; outer lip thin, a little oblique; pillar lip white 
internally, spread on the columella, and continuous with the 
margin of the outer lip. When recent it is covered with a fine 
pilous epidermis. 
Found principally in stagnant waters, ponds, and ditches, and 
by no means a plentiful species. 
3. PLanorsis L&vis, pl. XVIII, f. 7, 8, 9. 
Planorbis levis, Alder, Catalogue, Sup. Trans. Newcastle 
Nat. Hist. Soc., II, p. 337; Ib., Mag. Zool. and Bot., II, 
p- 113. 
Shell smooth, semitransparent; volutions equally convex both 
above and below; body volution rounded on the sides, large ; 
spire consisting of two or three small, compact, rounded yolu- 
tions; whole shell with nearly obsolete lines of growth, and 
of a brownish horn colour; aperture sublunated, or nearly 
circular. 
Discovered by Joshua Alder, Esq., Newcastle, in a pond on 
Holy Island, and has also been met with by him and the Rev. 
W. Mark, at Whitby, Northumberland; and has been found at 
Belfast by William Thompson, Esq. 
4. PLANorBis imBRicatus, pl. XIV, f. 46, 47, and pl. 
XVIII, f. 11—First Ed., pl. 41, f. 46, 47. 
Planorbis imbricatus, Miiller, Verm., II, p. 165; Draper- 
naud, p. 44, pl. 1, f.49, 50, 51; Pfeiffer, p. 84, pl. 3, f. 15; 
Brard, p. 163, pl. 6, f. 10, 11; Jeffreys, Linn. Tr., XVI, p- 
388; Alder, Mag. Zool. and Bot. II, p. 114; Turton, Man., 
p- 11, f.. 95; Forbes, Mal. Mon., p. 13; Thompson, Ann. and 
Mag. Nat. Hist., VI, p. 49; Planorbis nautileus, Fleming, 
Edin. Ency., VII, p. 69; Ib., Brit. An. p. 278; Turbo nau- 
tileus, Brown, Ency. Brit., VI, p. 457; Ib., Wernerian Mem., 
II, p. 522; Helia nautileus, Walker, f. 20, 21; Montagu, Test. 
Brit., p. 464, pl. 25, f. 5. 
Variety 1, pl. XVIII, f.10. Shell considerably smaller, with 
the imbricated lamine more distant. 
Planorbis cristatus, Drapernaud, p. 44, pl. 2, f. 1,82, 3; 
Pfeiffer, p. 84; Alder, Mag. Zool. and Bot., p. 114. 
Variety 2. With the lamine quite obsolete. 
Shell considerably depressed, pellucid, of a greenish or black- 
ish horn colour; sides of the body rounded; spire consisting of 
