115 



Dr. Leach erroneously quotes Draparnaud's PL Spi- 

 rorbis for this species. 



In stagnant waters, on aquatic plants. 



98. PLANORBIS Spirorbis. Shell thin, brown, slightly 

 concave on both sides, with six gradually increasing 

 and nearly equal volutions. 



Planorbis Spirorbis. Brard, p. 156. 

 Helix Spirorbis. Mont. p. 455. t. 25. f. 2. 



Shell in flatness and compactness of volutions much 

 resembling the PL Vortex, but is less and has 

 only six volutions ; the under surface is a little 

 concave in consequence of the volutions being 

 rounded, and the outer one not flattened into a 

 carinated edge ; and the aperture is rounded at 

 the upper end. Probably only a variety. 



In ponds and canals. 



A very minute species, apparently of this genus, is 

 found among drifted sand at Tenby and Falmouth. 

 It is slightly concave on both sides, without um- 

 bilicus, of three volutions, and marked with regular 

 raised transverse striae. It may have been brought 

 down by fresh-water currents ; but having, as yet, 

 never been found on land, nor alive, its generic 

 affinity must be left for future investigation. 

 i 2 



