MOLLUSCA. 
32 
two or three volutions, well divided by the suture line ; some- 
what largely umbilicate above and below ; body volution pro- 
vided with transverse spinous ribs, forming a regular crest round 
the centre of the sides ; aperture slightly ovate ; outer lip con- 
tinuous all round. Diameter the tenth of an inch. 
Not unfrequent in ponds and ditches, adhering to aquatic 
plants. 
Section II. — Volutions carinated. 
5. Planorbis carinatus, pi. XIV, f. 35, 36, 37« — First 
Ed., pi. 41, f. 35, 36, 37. 
Planorbis carinatus, Muller, Verm., II, p. 157; Drapernaud, 
p. 46, pi. 21, f. 13, 14, and 16; Pfeiffer, p. 76, pi. 4, f. 5, 6; 
Brard, p. 150, pi. 6, f. 3 ; Turton, Man., p. 106, f. 87 ; Alder, 
Mag. Zool. and Bot., II, p. 113; Thompson, Ann. and Mag. 
Nat. Hist., VI, p. 35; Helix complanata, Montagu, Test. Brit., 
Sup., p. 146, pi. 25, f. 4; Helix planata, Maton and Racket!, 
Linn. Tr., VIII, p. 189, ph 5, f. 14; Helix planorbis, Linne, 
Syst. Nat., I, p. 1242. 
Vaidety 1. Planorbis disciformis, Jeffreys, Linn. Tr., XVI, 
p. 521; Alder, Mag. Zool. and Bot., II, p. 113; Planorbis 
lutescens, Jeffreys, Linn. Tr., XVI, p. 385; Planorbis planatus, 
Turton, Man., p. 110, f. 92 ; Helix carinuta, Montagu, Test. 
Brit., p. 451, pi. 25, f. 1. 
Shell pale horn-coloured, subpellucid; with six rapidly in- 
creasing volutions, with a prominent obtuse keel on their outer 
edges, almost flat above, somewhat convex, and gradually bevil- 
ling off* towards the outer edge beneath, the outer volution 
suddenly increasing in size, and the hinder parts of each volu- 
tion rather convex ; aperture obliquely angular, contracted to a 
point beneath ; provided with a slight central umbilicus. Dia- 
meter about half an inch. 
This shell may be distinguished from the Planorbis margi- 
natus by the under side of the volutions being less inflated, and 
by their gradually bevilling off to the outer edge. In old shells 
the volutions become more inflated. This species is frequently 
covered with a thick brownish coating. It is also liable to mon- 
strosities. Sheppard, in the Linnean Transactions, vol. XIV., 
page 157, describes one with the volutions apart, similar to the 
Scalaria preciosa. 
Found in stagnant waters in many parts of Great Britain and 
Ireland. 
6. Planorbis marginatus, pi. XIV, f. 49, 40, 41. — First 
Ed., pi. 41, f. 39, 40, 41. 
Planorbis inarginatus, Drapernaud, p. 45, pi. 2, f. 11, 12, 
and 15; Brard, p. 152, pi. 6, f. 5; Rossmassler, Icon., II, pi. 2, 
f. 59; Alder, Mag. Zool. and Bot., II, p. 112; Turton, Man., 
p. 107, f. 87 ; Planorbis complanatus, Turton, Man., p. 108, f. 
88 ; Fleming, Brit. An., p. 278 ; Helix planorbis, Pennant, 
Brit. Zool., II, pi. 83, f. 123; Maton and Rackett, Linn. Tr., 
VIII, p. 188, pi. 5, f. 13; Helix complanata, Montagu, Test. 
Brit., p. 450, pi. 25, f. 4; Planorbis umbilicatus, Muller, Verm., 
II, p. 160; Jeffreys, Linn. Tr., XVI, p. 384. 
It is subject to the following varieties. 
Variety 1. Sides unequal, fragile, and glossy. 
Planorbis turgidus, Jeffreys, Linn. Tr., XVI, p. 383. 
Variety 2. Planorbis rhombeus, Turton, Man., p. 108, f. 
90 ; Planorbis Sheppardi, Leach, Moll., p. 149 ; Planorbis 
[Trachelipoda 
Drapernaldi, Jeffreys, Linn. Tr., XVI, p. 306; Helix Dra- 
pernaldi, Sheppard, Linn. Trans., XIV, p. 158. 
Variety 3. Destitute of a keel. 
Shell of a brownish horn-colour, semitransparent, slightly 
striated transversely, flat, or somewhat concave above, subum- 
bilicated below ; with five or six rapidly increasing, flat volu- 
tions, with a strong carina above, and ventricose and rounded to 
the margins beneath ; aperture rhombic, with the front rounded. 
Three-quarters of an inch in diameter. 
Found in stagnant waters. 
This is to be ^distinguished from P. carinatus by its being 
thicker, and the volutions more rounded, and more convex 
beneath on the margins ; in its more rounded aperture ; and in 
the keel being less prominent. 
The young shell is more rhomboidal, with the edges consi- 
derably thicker in proportion to its size, and is described and 
figured by Turton as a distinct species, under the name of Pla- 
norbis rhombeus. 
A remarkable monstrosity of this species was found by Mr. 
Thomas Stephens, in the pond of the College Botanic Garden 
of Dublin ; and is in the cabinet of my respected friend M. J. 
O’Kelly, Esq., of Rochestown House, near Cabinteely, Ireland. 
Plate XIV, f. 38. 
I figured and described this monstrosity in the Wernerian 
Memoirs, vol. II, p. 528, pi. 24, f. 10, under the name of Helix 
cochlea. It is thus described : — 
“ Shell of a dark horn-colour, with seven tapering, rounded 
volutions ; the three next the apex are twisted like a cork- 
screw, and terminate in a sharp point ; the five lower volutions 
slope gradually to a carinated ridge, which commences in the 
centre of the outer margin of the lip, and loses itself in the fifth 
volution, giving the volutions the appearance of being flat at 
bottom ; volutions slightly wrinkled obliquely across ; aperture 
somewhat angulated, oval, and a little compressed; lip very thin, 
and reflected on the columella at the base, where it is provided 
with a deep and wide umbilicus.” 
Turton described and copied my shell, in his Conch. Diet., 
under the name of Helix terebra; and in his Manuel, published 
in 1831, followed me, in the first edition of this work, in con- 
necting it with Planorbis marginatus. 
7. Planorbis vortex, pi. XIV, f. 44, 45. — First Ed., pi. 
41, f. 42, 43. 
Planorbis vortex, Muller, Verm., II, p. 158, var. a\ Draper- 
naud, p. 44, pi. 2, f. 4, 5 ; Brard, p. 154, pi. 6, f. 9 ; Lamarck, 
An. San. Vert., VI, p. 154; Pfeiffer, p. 79, ph 4, f. 7 ; Ross- 
massler, p. 104, pi. 2, f. 61 ; Jeffreys, Linn. Tr., XVI, p. 382; 
Turton, Man., p. 109, f. 91 ; Alder, Mag. Zool. and Bot., II, p. 
113; Forbes, Mai. Mon., p. 13; Thompson, Ann. and Mag. 
Nat. Hist., VI, p. 50 ; Planorbis compressus, Michaud, Compl., 
p. 81, pi. 16, f. 6 and 8 ; Helix vortex, Linne, Syst. Nat., I, p. 
1242; Montagu, Test. Brit., p. 454, pi. 25, f. 3; Brown, Wer- 
nerian Mem., II, p. 524; Ib., Ency. Brit., 6th Ed., VI, p. 458; 
Donovan, Brit. Sh., pi. 39, f- 1 ; Fleming, Brit. An., p. 278. 
Monstrosity. The aperture provided with a thickened inter- 
nal rib, Michaud, Compl., p. 80, pi. 16, f. 3, 4, 5; Rossmassler, 
Icon., I, p. 105, f. 62. 
Shell brownish horn-colour, transparent, very thin, flattened 
above, and a little concave below ; with six or seven gradually 
increasing, obliquely and transversely striated volutions, convex 
