Taken primarily from Kozloff, 1987, 1996 p. 200 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 1a | Shell with an oval or circular opening at the apex (photo) or with a slit just anterior to the apex (photo) | 2 |
| 1b | Shell without an oval or circular opening or slit (on the interior of the shell, however, there is a groove running from near the apex to the anterior margin; this takes the place of the exhalant opening typical of the family; ribs very coarse, with nodules and other roughenings; length sometimes slightly greater than 7 cm; subtidal, mostly on vertical rock cliffs) | Arginula bella
(Gabb, 1865) |
| 2a | Opening in shell oval or nearly circular, at the apex (photo) | 3 |
| 2b | Opening in shell a narrow slit, just anterior to the apex (photo) | 4 |
| 3a | Length of opening about one-third the length of the shell (photo); shell not more than 2 cm long, and covered by the mantle when the animal is alive | Fissurellidea bimaculata
Dall, 1871 |
| 3b | Length of opening about one-tenth the length of the shell; shell often 5 cm long, only a small, marginal portion of it covered by the mantle when the animal is alive | Diodora aspera
(Rathke, 1833) |
| 4a | Anterior slope of shell with a slight seam extending from the opening to the margin | 5 |
| 4b | Anterior slope of shell without a seam extending from the opening to the margin | 7 |
| 5a | Primary and secondary ribs of about the same size; margin nearly smooth, not obviously dentate where the ribs reach it (length up to about 2 cm) | Puncturella decorata
Cowan and McLean, 1968 |
| 5b | Primary and secondary ribs of distinctly different sizes; margin obviously dentate where the primary ribs reach it | 6 |
| 6a | With about 30 primary radial ribs (count near the apex), these separated, as they approach the margin, by 1-3 secondary ribs (when there are 3, the middle one may be nearly as prominent as the primary ribs, especially at the margin); marginal serrations, where the primary ribs reach the margin, not projecting more than 1 mm (length up to 3.5 cm) | Puncturella multistriata
Dall, 1914 |
| 6b | With 13-23 (usually about 16) sharp, raised primary ribs, most of these separated, as they approach the margin, by 3 or 4 faint secondary ribs; marginal serrations, where the primary ribs reach the margin, projecting 2-3 mm (length up to 4 cm) | Cranopsis cucullata
(Gould, 1846) (Was Puncturella cucullata) |
| 7a | Height generally equal to the width, and sometimes to the length; with about 27-33 radial ribs; length up to about 1 cm | Puncturella cooperi
Carpenter, 1864 |
| 7b | Height not quite equal to the width; with about 49-63 radial ribs; length up to 2 cm | Puncturella galeata
(Gould, 1846) |