Involute.] 



MOLLUSCA. 



31 



p. 85 ; Amplexa hypnorum, Fleming, Brit. An., p. 276 ; Lim- 

 nea turrita, Sowerby, Genera, f. 1 ; Nauta hypnorum, 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 Planorbis — 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, pi. XIV, f. 31, 32, 33 First Ed., 



pi. 41, f. 31, 32, 33. 



Planorbis corneus, Drapernaud, p. 43, pi. 1, f. 42, 43, 44 ; 

 Pfeiffer, p. 77, pi. 4, f. 3, 4 ; Lamarck, An. San. Vert., VI, pt. 

 2nd, p. 152; Brard, p. 147, pi. 6, f. 1, 2; Jeffreys, Linn. Tr., 

 XVI, p. 383 ; Fleming, Brit. An., p. 277 ; lb., 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, pi. 

 7, f. 113; Planorbis purpureas, Miiller, Verm., II, p. 154; 

 Planorbis similis, p. 166, young shell; Helix cornea, Donovan, 

 Brit. Sh., II, pi. 39, f- 1 ; Montagu, Test. Brit., p. 448; Brown, 

 Wernerian Mem., p. 524 ; lb., Ency. Brit., VI, p. 458 ; Helix 

 nana, Pennant, Brit. Zool., IV, p. 133, pi. 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 volutions are provided with fine 

 spiral striae. 



Found in slow rivers and stagnant ditches in England and 

 Ireland. 



2. Planorbis albus, pi. XIV, f. 52, 53 First Ed., pi. 41, 



f. 52, 53. 



Planorbis albus, Miiller, Verm., II, p. 164; Pfeiffer, p. 80, 



pi. 4, f. 9, 10; Leach, Moll., p. 156; Jeffreys, Linn. Tr., XVI, 

 p. 387 ; Fleming, Edin. Ency., VII, p. 69 ; lb., Brit. An., p. 

 278; Turton, Man., p. 114, f. 97; Alder, Mag. Zool. and Bot., 

 II, p. 113; Forbes, Mai. Mon., p. 13; Thompson, Ann. and 

 Mag. Nat. Hist., VI, p. 48 ; Planorbis hispidus, Drapernaud, 

 p. 43, pi. 1, f. 45, 46, 47, 48; Lamarck, An. San. Vert., VI, pt. 

 2nd, p. 154; Brard, p. 159, pi- 6, f. 6, 7; Helix alba, Montagu, 

 Test. Brit., p. 459, pi. 25, f. 7 ; Brown, Wernerian Mem., II, p. 

 524 ; lb., Ency. Brit., VI, p. 458. 



Variety 1 . Shell smooth, shining, and white. 



Planorbis glaber, Jeffreys, Linn. Tr., XVI, p. 3S7- 



Shell dextral, thin, pale yellowish-white, subpellucid, depres- 

 sed ; body volution very large, rounded on the sides ; spire 

 consisting of four rapidly decreasing volutions, which are equally 

 convex 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 stria?, 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. Planorbis ljevis, pi. XVIII, f. 7, 8, 9. 



Planorbis Icevis, Alder, Catalogue, Sup. Trans. Newcastle 

 Nat. Hist. Soc, II, p. 337; lb., 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 volu- 

 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, pi. XIV, f. 46, 47, and pi. 

 XVIII, f. 1 1— First Ed., pi. 41, f. 46, 47- 



Planorbis imbricatus, Miiller, Verm., II, p. 165; Draper- 

 naud, p. 44, pi. 1, f. 49, 50, 51 ; Pfeiffer, p. 84, pi. 3, f. 15 ; 

 Brard, p. 163, pi. 6, f. 10, 11 ; Jeffreys, Linn. Tr., XVI, p. 

 388; Alder, Mag. Zool. and Bot., II, p. 114; Turton, Man., 

 p. 1 1, f. 95 ; Forbes, Mai. Mon., p. 13 ; Thompson, Ann. and 

 Mag. Nat. Hist., VI, p. 49 ; Planorbis nautileus, Fleming, 

 Edin. Ency., VII, p. 69 ; lb., Brit. An., p. 278 ; Turbo nau- 

 tileus, Brown, Ency. Brit., VI, p. 457 ; lb., Wernerian Mem., 

 II, p. 522; Helix nautileus, Walker, f. 20, 21 ; Montagu, Test. 

 Brit., p. 464, pi. 25, f. 5. 



Variety 1, pi. XVIII, f. 10. Shell considerably smaller, with 

 the imbricated lamina more distant. 



Planorbis cristatus, Drapernaud, p. 44, pi. 2, f. 1 , 2, 3 ; 

 Pfeiffer, p. 84 ; Alder, Mag. Zool. and Bot., p. 114. 



Variety 2. With the lamina; quite obsolete. 



Shell considerably depressed, pellucid, of a greenish or black- 

 ish horn colour; sides of the body rounded; spire consisting of 



