165 



66. Ampullaria. A subglobose univalve ; the opening 

 longer than wide, and entire ; umbilicus at the base of the 

 columella, but no thickening of the left lip. Recent and 

 fossil. PI. v. fig. 14. 



67. Natica. A subglobose, umbilicated univalve ; open- 

 ing semicircular and entire ; the columella transverse, without 

 teeth, and callous externally, the callus contracting or even 

 covering the umbilicus. Recent and fossil. Pl.v. fig. 15. 



68. Nerita. A semiglobose univalve; the columella 

 nearly transverse and flat, with an acute and generally den- 

 tated edge. Recent and fossil. PI. v. fig. 16. 



69. Cyclostoma. A subdiscoidal or subpyramidal uni- 

 valve, with round turns, the last of which is the largest ; the 

 opening round, or nearly so; the edge circularly united, 

 forming a wide continuous margin. Recent and fossil. 

 PL v. fig. 17. 



70. Pupa. A somewhat cylindriform univalve ; the spire 

 long, the last turn not being larger than the preceding one ; 

 the opening irregular, rounded or oval ; the edges circularly 

 united. Recent. PI. iii. fig. 20. 



71. Scalaria. A turriculated univalve; the turns 

 rounded and nearly separate, with acute and longitudinal 

 raised ribs ; the opening nearly circular ; the margin unin- 

 terrupted and reflected. Recent and fossil. PI. v. fig. 18. 



72. Delphinula. A subdiscoidal, thick, pearly, and um- 

 bilicated univalve ; the turns generally muricated ; the 

 opening round; the margin circular and uninterrupted. 

 Recent and fossil. PI. v. fig. 19. 



73. Cirrus. A spiral and conical univalve, without a 

 columella ; funnel-shaped beneath ; volutions united. Fossil. 

 PI. v. fig. 20. 



74. Planorbis. A discoidal univalve ; spire depressed ; 

 turns visible on both sides ; opening entire, but diminished 

 by the projection into it of the preceding whirl. Recent 

 and fossil. PI. v. fig. 21. 



