32 



MOLLUSCA. 



[Tkachelipoda 



two or three volutions, well divided by the suture line ; some- 

 what largely umbilicate above and below; body volution pro- 

 wiled 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 cabinatus, pi. XIV, f. 35, 36, 37 — First 

 Ed., pi. 41, f. 35, 36, 37. 



Planorbis carinatus, Miiller, Verm., II, p. 157; Drapernaud, 

 p. 46, pi. 21, f. 13, 14, and 16; Pfeifler, 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 Rackett, 

 Linn. Tr., VIII, p. 189, pi. 5, f. 14; Helix planorbis, Linne, 

 Syst. Nat., I, p. 1242. 



Variety 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 carinata, 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 margin atus, pi. XIV, f. 49, 40, 41 — First 

 Kd., pi. 41, f. 39, 40, 41. 



Planorbis margmatus, 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, Miiller, Verm., 

 II, p. 160; Jeffreys, Linn. Tr., XVI, p. 384. 



It is subject to the following varieties. 



\ariely ]. 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 S Planorbis 



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 Wemerian 

 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, Miiller, 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, pi. 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 ; lb., 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 



