ESSENTIAL GENERIC CHARACTERS. XXVH 
a little angular or rounded,and contracted transversely: pillar 
placed obliquely. 
26. Turbo. Shell spiral, solid : aperture contracted, entire, 
more or less orbicular. 
27. Helix Shell spiral, more or less transparent and brittle : 
aperture contracted, roundish or crescent-shaped, 
28. Nerita. Shell spiral, gibbous, flattish underneath : 
aperture half orbicular; the pillar-lip transverse, flattish and 
truncate. 
29. Haliotis. Shell ear-shaped, almost entirely open, with 
a longitudinal row of orsfices towards the outer margin : spire 
lateral, flat upon the back. 
2. Without spire . 
30. Patella. Shell shaped like a bason, more or less conic, 
generally without spire. 
31. Dentalium. Shell linear, tubular, not divided into 
chambers, open at one or both ends. 
32.Serpula. Shell tubular, variously shaped, sometimes se¬ 
parated by internal divisions at irregular distances. 
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