109 



Shell about half an inch in diameter, rather thick, 

 brownish or purplish horn-colour, striolate : spires 

 four, the outer one much larger in proportion, and 

 faintly carinated near the base : aperture somewhat 

 rhombic, a little oblique, not quite so high as wide. 

 The carinated side is never a prominent rim, as in 

 PI. marginatus, and is sometimes very obscure. 



In slow streams, near Torquay in Devon. 



91. PLANORBIS Vortex. Shell brown, slightly con- 

 cave above and flat underneath, with six or seven 

 gradually increasing volutions, the outer one with 

 a sharp keel near the base. 



Planorbis Vortex. Drap. p. 44. t. 2.f. 4 7. 



Brard.p. 154. t. 6./. 9. 



Helix Vortex. Mont. p. 454. t. 25. f. 3. 

 Helix Planorbis. Da Costa, p. 65. t. 4./. 12. 



Shell three eighths of an inch in diameter, very flat and 

 thin, with six or seven gradually increasing volu- 

 tions, slightly concave above, and quite flattened 

 underneath so as to form a sharp edge round the 

 outer volution : aperture a little angular. 



In stagnant waters, common. 



