PLANORBIS. 233 



a. Spire Jiattish or slightly concave ; whorls not keeled, 

 rounded above and beloiv ; mouth semilunar, 

 (Coretus.) 



103. 1. Planorbis corneus. Horny Coll 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. ]. f. 42 — 44.; 

 Brard, p. 147. t. 6. f. 1, 2. ; Sowerhy, Genera, f. 1.; Jeffreys, 

 Linn, l^rans. xvi. ; Rnssm. Icon. i. t'. 86., ii. 14. t. 7. f. 113.; 

 Tiirton, Man. ed. 1. 112. f. 95.; Leach, Syn. 112.; Forbes 

 and Hanky, B. M. iv. 147. t. 125. f. 4, 5. — Planorbis purpu- 

 reas. Midler, Vei-m. ii. 154. (notvar.). — Helix cornu arietis. 

 Da Costa, B. C. 60. t. 4. f. 13. 



Junior, shell velvety, spirally striated : Planorbis similis. 

 Milller, 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 figured, 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 



Jaws of l.he Planorbis corneus magnified. 



a, Upper jaw ; b b, Rudimentary lateral jaws ; 

 c, Mouth closed. 



