270 PNEUMONOBRANCHIATA. 



* * * * Spire deeply umbilicated ; ivhorls rounded before 

 and behind, not keeled, close pressed. 



109. 10. PLANORBIS contortus. Twisted Coil Shell. 



(t. 8. f. 96.) Shell deeply umbilicate above, nearly 



flat beneath ; whorls eight, convex ; suture deep ; 



aperture very narrow crescent-shaped. 

 Planorbis contortus. Mutter, Verm. ii. 162. 



Drap. p. 42. t. 1. f. 39 41.; Jeffreys, Linn. 



Trans, xvi. 383.; Rossm. Icon. ii. 16. t. 7. 



f. 117.; Turton, Man. ed. 1. f. 96.; Brard, 



p. 157. t. 6. f. 1214. 

 Helix contorta. Linn. S. N. i. 1 244. ; Montagu, 



p. 457. t. 25. f. 6. 

 Helix umbilicata. Pulteney, Dorset, t. 20. f. 11. 



crassa. Da Costa, B. S. t. 4. f. 11. 



Inhab. ditches. Common. 



Animal grey or blackish. (Sturm, t. 41.) 



Shell about two tenths of an inch in diameter, and 

 one tenth in thickness, brown horn-colour, and when 

 free from accidental incrustations, exhibiting in water 

 a bronzed or gilt lustre; volutions five, remarkably 

 compact and equal in size; the upper surface with a 

 large and deep umbilicus; aperture very narrow 

 crescent-shaped, wider than high, only slightly pro- 

 duced on the under side. 



In describing this shell, Dr. Turton called that 

 the upper side which was considered the lower in the 

 other species, and vice versa. 



