89 
PLANORBIS. Lam. 
Gen. Cuar. Univalve, discoid, involute; without 
septa; spire flat or impressed ; aperture entire. 
'Tu1s 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 [ have omitted that 
part of Lamark’s Generic character which relates to it. 
The recent shells are inhabitants of fresh water. 
PLANORBIS equalis. 
TAB. CXL.—Fig. 1. 
Spec. Cuar. Equilaterally concave, with one 
obscure keel on the right side and two on the 
left; smooth; volutions exposed; aperture or- 
bicular, 
2 e]E-_-—ee— 
Tue 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 caring 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 
