Fresh-water Shells. AD 
folds of a bugle horn; this shape would be termed 
orbicular, from orbis—a sphere, or circular body. 
This is the largest Huropean species of Fresh-water 
Shells so constructed; it is often found in deep 
clear ditches, and yields a beautiful purple dye, 
which, however, soon becomes dull, and changes; 
it cannot be fixed, and is therefore valueless. The 
mouth of this shell, in fine specimens, is tinged 
with pale violet or lilac. 
There is another kind, the Keeled Planorbis 
(P. lurinatus), which has the outer edge of the shell 

finely ridged, or keeled; it is very small, and very 
plentiful in fresh-water, both running and stag- 
nant; where, too, is found the Common Physa 
(P. fontinalis), the latter word meaning a spring 
or fountain. This little mollusk is a quick and 
active traveller, it sometimes comes out of its shell 
and throws itself about in an extraordinary way, 
keeping fast hold by its foot; the generic name, 
Physa, would seem to have reference to the round, 
4, 
