12 



XX. PLANORBIS. COIL-SHELL. 



So named from the flattened and horizontal coil of 

 the volutions, by means of which the whole of the 

 gyrations may be seen on each of the sides. 



f 8/. Planorbis carinatus. Carinated Coil-shell. 



J. 8|^. Planorbis marginatus. Margined Coil-shell. 



S 8^. Planorbis complanatus. Flattened Coil-shell, 



DO. Planorbis rliombeiis. Rhombic Coil-shell. 



91. Planorbis Vortex. Wheel Coil-shell. 



92. Planorbis planatus. Edged Coil-shell. 



93. Planorbis fontanus. Fountain Coil-shell. 



94. Planorbis imbricatus. Nautilus Coil-shell. 



95. Planorbis corneus. Horn Coil-shell. 



96. Planorbis contortus. Twisted Coil-shell. 



97. Planorbis albus. White Coil-shell. 



98. Planorbis Spirorbis. Rolled Coil-shell. 



XXI. SEGMENTINA. SEGMENT-SHELL. 

 So called from the internal segments or partitions. 

 99. Segmentina nitida. Glossy Segment-shell, 



