LIMN^ADiE. 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., 

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

 f. 9. ; Lam. Hist. vi. i 54. ; Jeffreys, Linn. Trans. 

 xvi. 382.; Bossm. 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, Com.pl, 81. t. 16 



f. 6. 8. 

 Monstrosity. The mouth of the shell with a 



thickened internal rib. 

 Planorbis leucostomus. Midland, Compl. 80. t. 



16. f. 3, 4, 5.; Bossm. 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 



