20 LYMNiECEA. 



Section II. — Volutions cariymted, 



5. Planorbis carinatus, pi. Ill, f. 34, 35, 36. 

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



p. 46, pi. 21, f. 13, 14, and 16; Pfeiffer, p. 76, pi. 4, f. 5, 6 ; 

 Braid, p. 150, pi. 6, f. 3 ; Brown, Illust. Conch., p. 32, pi. 14, 

 f. 35, 36, 37; lb., First Ed., pi. 41, f. 35, 36, 37; Tiirton, 

 Man., p. 106, f. 87; Alder, Mag. Zool. and Bot., II, p. 113; 

 Thompson, Ann. and Mag. Nat. Hist., VI, p. 49 ; Helix com- 

 planata, 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 planorhis, Linne, Syst. Nat., I, p. 1242. 



Varietij 1, pi. IV, f. 7, Brown, Illust. Conch., p. 32, pi. 18, f. 

 24; 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 shght central umbilicus. Dia- 

 meter about half an inch. 



This shell may be distinguished from the Planorhis 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. Ill, f. 26, 27, 28. 

 Planorbis marginatus, Drapernaud, p. 45, pi. 2, f. 11, 12, 



and 15; Brard, p. 152, pi. 6, f. 5; Rossmassler, Icon., II, pi. 2, 

 f. 59; Brown, Illust. Conch., p. 32, pi. 14, f. 39, 40, 41 ; lb., 



