226 
LIMNiEAD^. 
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. J ef- 
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 fiuviatilis; 
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- i 
march’s character of Physa fontinalis is generally 
a small shell of a clear yellow colour, with a very 
short rounded spire formed of 3^ or 4 very gradu- I, 
ally enlarging whorls, the suture of the last being j 
more oblique than the rest, and with a subacute tip. 
