Taken primarily from Kozloff, 1987, 1996 p. 279 (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 | Hinge plate with lateral teeth (these may be small) in addition to the cardinal teeth | 2 |
| 1b | Hinge plate without lateral teeth | 5 |
| 2a | Shell about twice as long as high; length commonly more than 1 cm | 3 |
| 2b | Shell much less than twice as long as high; length up to 1 cm or slightly more | 4 |
| 3a | Interior of both valves with a ridge just behind the scar of the anterior adductor muscle; length up to about 2 cm | Tellina (Angulus) modesta |
| 3b | Neither valve with a ridge behind the scar of the anterior adductor muscle; length up to about 5 cm | Tellina (Moerella) bodegensis |
| 4a | Shell slightly more than 1.5 times as long as high; valves becoming narrowed toward the posteroventral corner; exterior white to pink | Tellina (Angulus) carpenteri |
| 4b | Shell about 1.3 times as long as high; valves rounded posteriorly; exterior whitish or yellow, but interior often pink | Tellina (Cadella) nucleoides |
| 5a | Length about twice the height; rare | Macoma (Psammacoma) yoldiformis |
| 5b | Length much less than twice the height; common intertidal and subtidal species | 6 |
| 6a | Posterior portions of both valves distinctly bent to the right (photo) | Macoma (Heteromacoma) nasuta |
| 6b | Posterior portions of valves not bent to the right | 7 |
| 7a | Periostracum polished, usually transparent; hinge ligament not more than 1/4 the length of the slope from the umbones to the posterior end; length commonly exceeding 5 cm, and sometimes attaining 10 cm | Macoma (Rexithaerus) secta |
| 7b | Periostracum not polished or transparent; hinge ligament at least 1/3 the length of the slope from the umbones to the posterior end; length not often exceeding 5 cm | 8 |
| 8a | Outline of valves almost perfectly oval; the posterior end nearly as rounded as the anterior end; valves (especially the interior) often yellow, pink, or bluish; length to about 2 cm | Macoma (Macoma) balthica |
| 8b | Outline of valves not almost perfectly oval, the posterior end being narrowed and less rounded than the anterior end; valves whitish, except for the brown periostracum; length up to about 5 cm | Macoma (Heteromacoma) inquinata |
Macoma nasuta
Tellina (Angulus) modesta