PLANOKBIS. 
233 
a. Spire Jlattish or slightly concave ; whorls not heeled^ 
rounded above and beloiv ; mouth semilunar, 
(Coretus.) 
103. 1. Planorbis corneus. Horny Coil Shell. — 
Shell nearly flat above, deeply umbilicate be- 
neath, showing the convex whorls ; whorls 
six, rounded, striated ; aperture semicircular, 
(t. 8. f. 95.) 
Helix cornea. Linn, S. N. 1243. ; Mont, Test, Brit, 449.— 
Planorbis corneus. Drap, Hist. p. 43. t. I. f. 42 — 44. ; 
Brard, p. 147. t. 6. f. 1, 2. ; Sowerbi/, Genera., f. 1.; Jeffreys., 
Linn, Trans, xvi. ; Rossm, Icon, i. f. 86., ii. 14. t. 7. f. 113. ; 
Turton., Man. ed. 1. 112. f. 95. ; Leach., Syn, 112. ; Forbes 
and Hanley^ B, M, iv. 147. 1. 125. f. 4, 5. — Planorbis purpu- 
reus. Muller., Verm, ii. 154. (not var.). — Helix cornu arietis. 
Da Costa., B, C, 60. t. 4. f. 13. 
J unior, shell velvety, spirally striated : Planorbis similis. 
Muller, Verm, 166. — ■ Helix nana. Penn, B, Z, f. 125. 
In muddy streams and ditches. 
Animal black. {Sturm, t. 40.) The mouth is 
red-brown. When the mouth is in movement, two 
small tubercles are to be observed on each side, 
which are the rudiments of lateral jaws, not found 
in other species of the genus, but found in the genus 
Lymnea, 
The teeth are flgured, Otto Goldfuss, 48. t. 7. f. b . ; 
jaws three, — the upper distinct, crescent-shaped, cre- 
nulated, lateral rudimentary, flexuous (fig. 57. ). The 
Fig, 57 . animal when irritated emits from its 
a 
Jaws of the Planorbis corneus magnified. 
a, Upper jaw ; h b, Rudimentary lateral jaws ; 
c, Mouth closed. 
