INVOLUTE. ] 
before and flattened behind, and furnished with a sharp carina ; 
aperture subtriangular, rhomboidal, white and thickened inter- 
nally, and slightly compressed. Diameter about three-eighths 
of an inch. 
Found in ditches and other stagnant waters in Great Britain 
and Ireland. 
8. PLANoRBIS sPIRORBIS, pl. XIV, f. 42, 43.—First Ed., 
pl. 41, f. 44, 45. 
Planorbis spirorbis, Miller, Verm., II, p. 161; Brard, p. 
156; Sturm, Fauna, pl.45; Turton, Man., p. 115, f. 98; Alder, 
Mag. Zool. and Bot., II, p. 113; Forbes, Mal. Mon., p. 13; 
Thompson, Ann. and Mag. Nat Hist., VI, p. 50; Planorbis 
vortex, Drapernaud, Moll., p. 45, pl. 2, f. 6, 7; Jeffreys, Linn. 
Tr., XVI, p. 382; Pfeiffer, p. 79, pl. 4, f.8; Helix spirorbis, 
Montagu, Test. Brit., Sup., p. 455, pl. 25, f. 2; Maton and 
Rackett, Linn. Tr., VIII, p. 191; Brown, Wernerian Mem., 
II, p. 524; Ib., 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 striz ; aperture subrotund, and rounded below. 
Diameter about a quarter of an inch. 
Found in ditches and stagnant waters. 
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 vortez, in proportion to its size. 
Section III.—Shell shining, translucent ; spire deeply um- 
bilicate ; volutions provided with a slight carina. 
9. Panorsis nitiDUus, pl. XIV, f. 48, 49.—First Ed., pl. 
41, f. 48, 49. 
Planorbis nitidus, Miiller, Verm., II, p. 263; Pfeiffer, p. 82, 
pl. 4, f. 12, 13; Fleming, Brit. An., p. 278; Jeffreys, Linn. Tr., 
XVI, p. 389; Alder, Mag. Zool. and Bot., II, p. 114; Thomp- 
son, Ann. and Mag. Nat. Hist., VI, p. 51; Planorbis lenticula- 
ris, Sturm, Fauna, VI, pl. 8, f. 16; Planorbis fontanus, Turton, 
Man., p. 110, f.93; Planorbis complanatus, Drapernaud, Moll., 
p- 47, pl. 2, £. 20, 21, 22; Rossmassler, Icon., II, p. 16, pl. 7, f. 
116; Brard, p. 161, pl. 6, f.4; Helix fontana, Lightfoot, Phil. 
Trans., LXXVI, pl. 2, f. 1; Montagu, Test. Brit., p. 462, pl. 6, 
f. 6; Maton and Rackett, Linn. Tr., VIII, p. 192; Brown, 
Wernerian Mem., II, p. 524; Helix lenticularis, V. Alten., p. 
35, pl. 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 ; 
I 
MOLLUSCA. 33 
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 umbilicated. 
10. Pxanorpis conTrortus, pl. XIV, f. 33, 34.—First 
Ed., pl. 41, f. 33, 34. 
Planorbis contrortus, Miiller, Verm., I, p. 162; Draper- 
naud, Moll., p. 42, pl. 1, f. 39, 40, 41; Sturm, Fauna, pl. 3, f. 
4; Pfeiffer, p. 81, pl. 4, f. 11; Lamarck, An. San. Vert., VI, 
pt- 2nd, p. 154; Jeffreys, Linn. ‘Tr., XVI, p. 383; Fleming, 
Brit. An., p.277; Forbes, Mal. Mon., p. 13; Rossmassler, Icon., 
II, p. 16, pl. 7, f. 117; Turton, Man., p. 113, f. 96; Brard, p- 
157, pl. 6, f. 12, 13, 14; Alder, Mag. Zool. and Bot., II, p. 
114; Thompson, Ann. and Mag. Nat. Hist., VI, p. 51; Helic 
contorta, Linné, Syst. Nat., I, p. 1244; Montagu, Test. Brit., 
p- 457, pl. 25, f. 6; Donovan, Brit. Sh., IL, pl. 99; Brown, 
Ency. Brit., 6th Ed., VI, p. 458; Ib., Wernerian Mem., II, p. 
524; Heli wmbilicata, Pulteney, Cat. Dorset, p. 47, pl. 20, f. 
11; Helix crasius, Da Costa, Brit. Sh., p. 66, pl. 4, f. 11. 
Shell thick, depressed, of a brown horn-colour, sometimes 
rufous or chestnut; with five or six greatly compressed, equal 
sized, compact, close-set volutions, the outer one rounded, the 
others on the wider side rise nearly to an edge, and are divided 
by a deep suture, having a subumbilicus in the centre; upper 
side largely and deeply umbilicated, exhibiting every yolution, 
spirally descending to the bottom; aperture crescent-shaped, 
compressed, and clasping the body volution. Diameter a quar- 
ter of an inch; and somewhat more than a tenth of an inch in 
thickness. 
Common in ditches and stagnant pools. 
Genus 41.—SEGMENTINA.—Fleming. 
Shell divided internally by transverse septa into several 
chambers, which communicate into each other by triradiated 
apertures. 
1. SEGMENTINA LINEATA, pl. XIV, f. 50, 51.—First Ed., 
pl. 41, f. 50, 51. 
Segmentina lineata, Fleming, Brit. An., p. 279; Ib. Ency. 
Brit., pl. 367, f. 8; Planorbis nitidus, Miiller, II, p. 163; Dra- 
pernaud, Moll., p. 46, pl. 2, f. 17, 18, 19; Rossmassler, Icon., 
II, p. 15, pl. 7, f. 114, 115; Turton, Man., p. 116, f. 91; Pla- 
norbis nautileus, Fleming, Edin. Ency., VII, p. 69; Kickx, 
Moll. Barb., p. 66; Planorbis lineatus, Alder, Mag. Zool. and 
Bot., I, p. 114; Nautilus lacustris, Lightfoot, Phil. Trans., 
XXVI, pl. 1, figs. 1 to 7; Montagu, Test. Brit., p. 191, pl. 6, f. 
3; Hemithalamus lacustris, Leach, Moll., p. 137; Helix lineata, 
Walker, Test. Min. Rar., pl. 1, f. 28. 
Shell compressed, subcarinated, extremely pellucid, smooth 
and shining, horn-coloured, sometimes reddish-brown; upper 
surface conyex; apex depressed, concave, and deeply umbili- 
cate; with four volutions, the apical one lost in the depression, 
the outer one very large, these are bordered on their outer 
edge with a whitish spiral band, which terminates in the centre 
