242 
LIMNJEAD^. 
109. 7. Planoebis vortex. Whorl Coil Shell. — 
Shell brown^ pellucid^ thin, flat above, slightly 
and regularly concave beneath, with six or 
seven gradually increasing sharply keeled 
volutions, which are convex before and flat 
behind ; mouth rhombic, compressed, (t. 8. 
f. 91.) 
Helix vortex. Linn. S. N. i. 1242. ; Mont. T. B. p. 454. t. 25. 
f. 3. — Planorbis vortex. Muller, Verm. ii. 158. ; var. 
Drap. p. 44. t. 2. f. 4, 5. ; Brard., p. 154. t. 6. f. 9. ; Lam. 
Hist.Vi. 154.; Jeffreys, Linn. Trans, xvi. 382.; Bossm. Leon. 
104. t. 2. f. 61.; Sturm, Fauna, t. 44.; Turton, Man ed. 1. 
109. f. 91. Leach, Syn. Moll. 112.; Forbes and Hanley, 
B. M. iv. 157. t. 127. f. 6, 7, 8. — Helix planorbis. Da 
Costa, p. 65. t. 4. f. 12. — Planorbis compressus. Michaud, 
Compl. 81. t. 16. f. 6. 8. — Planorbis tenellus. Studer, 
Cat. 92. 
Yar. 1., the mouth of the shell with a thickened internal rib : 
Planorbis leucostomus. Michaud, Compl. 80. t. 16. f. 3, 4, 5.; 
Bossm. Lcon.i. 105. f. 62. — Planorbis rotundatus. Poir. 
Prod. 93.; Moq. Tand. ii. 435. t. 30. f. 38 — 46. — Planorbis 
vortex Drap. Hist. 45. t. 2. f. 6, 7. 
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 epipJiragm^ within 
which it lies secure under the mud and weeds, 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. 
Muller long ago pointed out the white and thick- 
ened aperture as an occasional character of this shell, 
