89 
PLANORBIS. Lam. 
Gen. Char. Univalve, discoid, involute ; without 
septa ; spire flat or impressed ; aperture entire. 
This Genus has been well separated from Helix of 
Linneus, it contains shells composed of a simple tube 
curved into a Volute; in many species the latter whorls 
partly embrace those preceding, but this is not the case 
with several shells which otherwise have a natural 
relation to the type of the Genus, so I have omitted that 
part of Lamark’s Generic character which relates to it. 
The recent shells are inhabitants of fresh water. 
PLANORBIS equalis 8 
TAB, CXL .—Fig. l. 
Spec, Char, Equilaterally concave, with one 
obscure keel on the right side and two on the 
left ; smooth ; volutions exposed ; aperture or- 
bieular* 
The inside of the tube composing this is perfectly round 
but the shell is thicker towards the front, so as to make 
the outer edge of the mouth obtusely obovate; the con-* 
centric carinae are very obtuse and inconspicuous. There 
is a slight impression of the preceding whorl in the sub- 
stance of the last, 
A specimen of Limestone from Kendal afforded me 
this shell, it is replaced or cast in white Carbonate of 
Lime or Spathose Limestone, and is filled up with darker 
amorphous Limestone* which is somewhat of a redder 
