| Macrocallista (Chionella) omissa Pilsbry & Lowe, 1932 |
| Macrocallista maculata (Linnaeus, 1758) |
| Macrocallista nimbosa (Lightfoot, 1786) |
| Megapitaria Grant & Gale, 1931 |
| Megapitaria aurantiaca (G. B. Sowerby I, 1831) |
| Megapitaria maculata (Linnaeus, 1758) |
| Megapitaria squalida (G. B. Sowerby I, 1835) |
| Mercenaria Schumacher, 1817 |
| Mercenaria campechiensis (Gmelin, 1791) |
| Mercenaria campechiensis subsp. campechiensis (Gmelin, 1791) |
| Mercenaria campechiensis subsp. texana (Dall, 1902) |
| Mercenaria mercenaria (Linnaeus, 1758) |
| Meretricinae Gray, 1847 |
| Meretrix Lamarck, 1799 |
| Meretrix aresta Dall & Simpson, 1901 |
| Meretrix culebrana Dall & Simpson, 1901 |
| Meretrix simpsoni Dall, 1895 |
| Mysia Lamarck, 1818 |
| Mysia nucleiformis Wagner, 1840 |
| Nioche Hertlein & Strong, 1948 |