226 LIMN2EAM:. 



1836, t. 9. f. 10, 11. They are very unlike the 

 teeth of Lymnea. 



Shell nearly half an inch long, and half as much 

 broad, very thin and fragile ; spire extremely short, 

 of four volutions, the lower one much inflated, the 

 others small and ending obtusely ; aperture covering 

 nearly the whole of the shell ; pillar slightly sinuate 

 and white, not reflected. 



This shell varies considerably in shape. Mr. Jef- 

 freys distinguished four varieties. Some have the 

 spire elongated considerably more than the rest. 

 Dr. Turton (Conch. Diet.) described a small sub- 

 globose specimen under the name of Bulla fluviatilis ; 

 but it probably is only a young specimen of the 

 common state. 



It is the young specimens of these shells alone 

 which agree with the Linnaean and Lamarckian cha- 

 racter of the species in the shortness of the spire ; for 

 as the shell increases in size, the whorls are gradually 

 turned more obliquely down the axis, so that the 

 older shells have a longer spire in proportion than 

 the young ones. 



There are nevertheless two very distinct varieties, 

 which may prove to be distinct species, and indeed 

 have been considered so by several of my friends, as 

 Mr. Fryer and Mr. Hinks, who study these animals. 

 The one which agrees best with Linnaeus's and La- 

 marck's character of Physa fontinalis is generally 

 a small shell of a clear yellow colour, with a very 

 short rounded spire formed of 3 J or 4 very gradu- 

 ally enlarging whorls, the suture of the last being 

 more oblique than the rest, and with a subacute tip. 



