LIMN^ADJE. 267' 



106. 7. PLANORBIS vortex. Whorl Coil Shell, (t. 8. 

 f. 91.) Shell brown, pellucid, thin, flat above, 

 slightly and regularly concave beneath, with six 

 or seven gradually increasing sharply keeled volu- 

 tions, which are convex before and flat behind 

 mouth rhombic, compressed. 



Planorbis vortex. Mutter, Verm. ii. 158.; var. a., 

 Drap. p. 44. t. 2. f. 4, 5.; Brard, p. 154. t. 6. 

 f. 9.; Lam. Hist. vi. 154.; Jeffreys, Linn. Trans. 

 xvi. 382.; Rossm. Icon. 104. t. 2. f. 61.; Sturm, 

 Fauna, t. 44. ; Turton, Man. ed. 1. 109. f. 91. 

 Helix vortex. Linn. S. N. i. 1242.; Mont. p. 



454. t. 25. f. 3. 



Helix planorbis. Da Costa, p. 65. t. 4, f. 12. 

 Planorbis compressus. Michaud, Compl. 81. t. 16 



f. 6. 8. 

 Monstrosity. The mouth of the shell with a 



thickened internal rib. 

 Planorbis leucostomus. Michaud, Compl. 80. t. 



16. f. 3, 4, 5.; Rossm. Icon. i. 105. f. 62. 

 In stagnant waters. 

 Animal violet-brown. 



Shell three eighths of an inch in diameter, very 

 flat and thin, with six or seven gradually increasing 

 volutions, slightly concave above, and quite flattened 

 underneath, so as to form a sharp edge round the 

 outer volution ; aperture a little angular. 



In summer, when the ditches are dry, this animal 

 closes up its shell with a white epiphragm, within 

 which it lies secure under the mud and weed, in a 

 state of torpidity, until the ditches are again filled 

 with water. The animal then thickens the internal 

 margin of the shell, forming a permanent white rim. 

 N 2 



