Involute.] 



MOLLUSCA. 



33 



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, pi. XIV, f. 42, 43. — First Ed., 

 pi. 41, f. 44, 45. 



Planorbis spirorbis, Miiller, Verm., II, p. 161 ; Brard, p. 

 156; Sturm, Fauna, pi. 45; Turton, Man., p. 115, f. 98; Alder, 

 Mag. Zool. and Bot., II, p. 113; Forbes, Mai. Mon., p. 13; 

 Thompson, Ann. and Mag. Nat Hist., VI, p. 50 ; Planorbis 

 vortex, Drapernaud, Moll., p. 45, pi. 2, f. 6, 7 ; Jeffreys, Linn. 

 Tr., XVI, p. 382 ; Pfeiffer, p. 79, pi- 4, f. 8 ; Helix spirorbis, 

 Montagu, Test. Brit., Sup., p. 455, pi. 25, f. 2; Maton and 

 Rackett, Linn. Tr., VIII, p. 191 ; Brown, Wernerian Mem., 

 II, p. 524; lb., 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 stria? ; 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 vortex, in proportion to its size. 



Section III. — Shell shining, translucent ; spire deeply um- 

 bilicate ; volutions provided with a slight carina. 



9. Planorbis nitidus, pi. XIV, f. 48, 49 — First Ed., pi. 

 41, f. 48, 49. 



Planorbis nitidus, Miiller, Verm., II, p. 263 ; Pfeiffer, p. 82, 

 pi. 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, pi. 8, f. 16; Planorbis fontanus, Turton, 

 Man., p. 110, f. 93; Planorbis complanatus, Drapernaud, Moll., 

 p. 47, pi. 2, f. 20, 21, 22; Rossmassler, Icon., II, p. 16, pi. 7, f- 

 116; Brard, p. 161, pi. 6, f. 4; Helix fontana, Lightfoot, Phil. 

 Trans., LXXVI, pi. 2, f. 1 ; Montagu, Test. Brit., p. 462, pi. 6, 

 f. 6; Maton and Rackett, Linn. Tr., VIII, p. 192; Brown, 

 Wernerian Mem., II, p. 524 ; Helix lenticularis, V. Alten., p. 

 35, pi. 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 

 •ide ; 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 



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. Planorbis contrortus, pi. XIV, f. 33, 34. — First 

 Ed., pi. 41, f. 33, 34. 



Planorbis contrortus, Miiller, Verm., II, p. 162; Draper- 

 naud, Moll., p. 42, pi. 1, f. 39, 40, 41 ; Sturm, Fauna, pi. 3, f. 

 4; Pfeiffer, p. 81, pi. 4, f. 11 ; Lamarck, An. San. Vert., VI, 

 pt. 2nd, p. 154; Jeffreys, Linn. Tr., XVI, p. 383; Fleming, 

 Brit. An., p. 277; Forbes, Mai. Mon., p. 13; Rossmassler, Icon., 

 II, p. 16, pi. 7, f. 117 ; Turton, Man., p. 113, f. 96 ; Brard, p. 

 157, pi. 6, f. 12, 13, 14 ; Alder, Mag. Zool. and Bot., II, p. 

 114; Thompson, Ann. and Mag. Nat. Hist., VI, p. 51 ; Helix 

 contorta, Linne, Syst. Nat., I, p. 1244; Montagu, Test. Brit., 

 p. 457, pi. 25, f. 6 ; Donovan, Brit. Sh., Ill, pi. 99 ; Brown, 

 Ency. Brit., 6th Ed., VI, p. 458 ; lb., Wernerian Mem., II, p. 

 524 ; Helix umbilicata, Pulteney, Cat. Dorset, p. 47, pi. 20, f. 

 11 ; Helix crasius, Da Costa, Brit. Sh., p. 66, pi. 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 volution, 

 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, pi. XIV, f. 50, 51. — First Ed., 

 pi. 41, f. 50, 51. 



Segmentina lineata, Fleming, Brit. An., p. 279 ; lb., Ency- 

 Brit., pi. 367, f. 8; Planorbis nitidus, Miiller, II, p. 163; Dra- 

 pernaud, Moll., p. 46, pi. 2, f. 17, 18, 19; Rossmassler, Icon., 

 II, p. 15, pi. 7, f. 114, 1 15; Turton, Man., p. 116, f. 91; Pla- 

 norbis nautiletis, Fleming, Edin. Ency., VII, p. 69; Kickx. 

 Moll. Barb., p. 66 ; Planorbis lineatus, Alder, Mag. Zool. and 

 Bot., II, p. 114; Nautilus lacustris, Lightfoot, Phil. Trans., 

 XXVI, pi. 1, figs. 1 to 7; Montagu, Test. Brit., p. 191, pi- 6, f. 

 3 ; Hemithalamus lacustris, Leach, Moll., p. 137 ; Helix lineata, 

 Walker, Test. Min. Rar., pi. 1, f. 28. 



Shell compressed, subcarinated, extremely pellucid, smooth 

 and shining, horn-coloured, sometimes reddish-brown; upper 

 surface convex; 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 



