FAMILY LYMNiEACEA. 



139 



leated appearance arises from the enlargement and diffusion, after 

 the first two or three whorls, of the longitudinal striae. The spire 

 is so much immersed that the inner edges of the whorls, usually 

 forming the wall of the umbilicus in spiral shells, are pushed into a 

 nearly flattened disk. 



Planorbis corneas has a wide range on the Continent, passing into 

 Siberia, and over the islands of the Mediterranean into North 

 Africa; but it is curiously partial in Britain. In the ponds and 

 ditches of the eastern, south-eastern, and midland counties of Eng- 

 land, and of the south-eastern parts of Ireland, Planorbis corneus is 

 not uncommon ; but it does not appear in Cornwall or Devon, nor 

 in Scotland. In colour, the sheU is mostly of a livid ash-grey, 

 passing into olive. Sometimes it is of a dark reddish olive, and 

 sometimes entirely white. 



2. Planorbis albus. Wliite Planorbis. 



Shell ; rather depressed, thin, whitish horny, covered with a scarcely 

 perceptible hairy epidermis, less concave above than 

 below, lower concavity a broadly excavated umbi- q^ 



licus, spire moderately immersed, whorls four and 

 a half to five, longitudinally very finely thread- 

 ridged, interstices faintly decussated with trans- 

 verse striae ; aperture obbquely lunar ovate. 



Planorbis albus, Miiller (1774), Verm. Mist, part 2. p. 164. 



Planorbis villosus, Poiret (1801), Coq. de V Aisne, Prod. p. 

 95. 



Planorbis hispidus, Vallot (1801), Cat. Moll, dela Cote-d'Or, 



p. 5. 



Helix Draparnaudi, Sheppard (1825), Trans. Linn. Soc. vol. xiv. p. 158. 



Planorbis reticulatus^m (1826), Hist. Nat. Europ. Merid. vol. iv. p. 98. 



Planorbis Drapamaldi, Jeffreys (1830), Trans. Linn. Soc. vol. xvi. p. 386. 



QyrauUs hispidus, Hartmarm (1841), Erd. und Siissw. Gast. pi. xxv. 



Planorbis (Gyraulus) albus, Mo ^um-Tanclon (1855), vol. h. p. 440.pl. 

 xxxi. f. 12 to 19. 



Hob. Throughout Europe. Siberia. North Africa. (Everywhere com- 

 mon on water-plants.) 

 This is a thinly compressed form of Planorbis, in which the 



whorls of the shell are longitudinally thread-striated, somewhat 



after the manner of the early whorls of the preceding species, and 



