«ver ; an arrangement however in which he was not fol- 

 lowed by any of the distinguished naturalists who succeed- 

 ed him. 



Lamarck in his earlier works, placed the genus near 

 Ampularia, deceived perhaps by the equivocal characters 

 of A. cornu arietes, which he supposed to be a Planorbis, 

 but he afterwards referred the genus to its true place in 

 the family of Pulmonea Aquatica. next to Limneus. Like 

 all the species of tills family the Planorbis never reside in 

 deep water, but frequent the shores where they can resort 

 to the surface to inhale tlie air. They inhabit fresh water 

 and abound in various parts of the globe. 



The shell of Planorbis has the appearance of being si- 

 nistral, and this character has been almost universally sta- 

 ted in the generic definition ; several conchologists, how- 

 ever, are now of the opinion that it is dextral, notwithstand- 

 ing the sinistral form of the animal. Des Moulins in the 

 '• Actes de la Soc. Linn, de Bordeaux," says that " the shell 

 of the Planorbis is essentially dextral." Deshayes in his 

 account of this genus says that it is only necessary to exa- 

 mine the greater number of the species and to compare 

 them with the d«xtral Limneus and sinistral Physa, to be 

 convinced, that in the normal position, the shell of Pla- 

 norbis is truly dextral ; but that the animal is really sinis- 

 tral ; and he thinks we ought rather to admit that a sinis- 

 tral animal has a dextral shell, than that the aperture is 

 not in the normal direction, cci responding wilh that of all 

 shells yet discovered ; and that there is an evident contra- 

 diction between the animal and iis shell, as is also exhibit- 

 ed in the Ilaliotis and probably in Ancylus. 

 p;. 54. 



