142 BRITISH MOLLUSKS. 



all parts of oiir islands, and it extends on the Continent from the 

 extreme north to south, passing into Algeria. 



5. Planorbis carinatus. Keeled Planorbis. 



Shell ; very depressed, concave above, the spire being a little im- 

 mersed, concavely flattened below, pale horny, 

 smooth, glossy, whorls five, rounded above, con- 

 vex below, strongly keeled rather below the mid- 

 dle ; aperture obliquely ovate, somewhat rhom- 

 boidal. 

 Helix planorbis, Linnaeus (1758), Si/st. Nat. 10th edit. p. 769 



(not of Da Costa). 

 Planorbis carinatus, Miiller (1774), Verm. Hist, part ii. p. 175 (not of 



Studer). 

 Helix limbata, Da Costa (1778), Test. Brit. p. 63. pi. iv. f. 10 (not of 



Draparnaud). 

 Planorbis acutus, Poiret (1801), Coq. de I'Aisne, Prod. p. 91. 

 Helix carinata, Montagu (1803), Test. Brit. p. 450. 

 Helix planata, Maton and Eackett (1807), Trans. Linn. Soc. vol. viii. 



p. 109. pi. v. f. 14. 

 Planorbis umbilicatus, Studer (1820), Kurz. Verz. p. 92 (not of Miiller). 

 Planorbis lutescens and disciformis, Jeffreys (1830), Trans. Linn. Soc. vol. 



xvi. p. 385 and 521. 

 Planorbis planatus, Turton (1831), Man. p. 110. f. 92. 

 Planorbis (Qyrorbis) carinatus, Moquin-Tandon (1855), Hist. Moll. vol. ii. 



p. 431. pi. xxx. f. 29 to 33. 

 Hah. Europe, widely diffused but partial. Siberia. England and Ire- 

 land. Chiefly in eastern and south-eastern counties. (In stagnant 

 marshes.) 

 This and the following species require to be examined together. 

 They resemble each other so closely as scarcely to show any per- 

 ceptible difference ; but there are differences and they are constant. 

 On comparing our figures of the shells, which are roughly drawn 

 but characteristic, it will be seen that P. carinatus is smaller and 

 more finely striated than P. complanatus, and that the encircling- 

 keel is not so close to the basal edge. The lower disk in the upper 

 figure of P. carinatus is seen just below the keel, which is not the 

 case in the corresponding figure of P. complanatus, and the keel 

 by a correlation of growth winds more conspicuously into the aper- 



