• Helisoma Sandberger, 1880 † (uncertain) [Family: Mollusca (awaiting allocation)]
• Helisoma Swainson, 1840 [Family: Planorbidae]
• Mecasoma Chemsak & Linsley, 1974
• Mecosoma Dallas, 1851 (uncertain)
• Medistoma Iredale, 1941 (unaccepted > nomen nudum)
• Megasoma Boisduval in Feisthamel, 1832 accepted as Streblote Hübner, 1820 [Family: Lasiocampidae]
• Megasoma Kirby, 1825 [Family: Scarabaeidae]
• Megistoma Tryon, 1883 † accepted as Megistostoma Gabb, 1864 †
• Meistoma Sandon, 1941 accepted as Meiostoma Sandon, 1941
• Mejosoma Puton, 1875 (unaccepted)
• Melasma H. Adams & A. Adams, 1854 [Family: Thiaridae]
• Melasma P.J. Bergius, 1767 [Family: Orobanchaceae]
• Melasma Wollaston, 1864 accepted as Melasmana Strand, 1935 [Family: Tenebrionidae]
• Melasoma Stephens, 1831 accepted as Chrysomela Linnaeus, 1758 [Family: Chrysomelidae]
• Melasoma Swainson, 1837 (uncertain) [Family: Aves (awaiting allocation)]
• Melastoma Linnaeus, 1753
• Melatoma Gray, 1847 (uncertain) [Family: Mollusca (awaiting allocation)]
• Melatoma Swainson, 1840 accepted as Clionella Gray, 1847 [Family: Clavatulidae]
• Meleoma Fitch, 1856
• Meliboea Forbes, 1838 accepted as Melibe Rang, 1829 [Family: Tethydidae]
• Meliboea Robineau-Desvoidy, 1863 accepted as Melibaea Robineau-Desvoidy, 1848 accepted as Phebellia Robineau-Desvoidy, 1846 [Family: Tachinidae]
• Melidora Lesson, 1830 [Family: Halcyonidae]
• Melidora Noronha ex R.A. Salisbury, 1817 (uncertain) [Family: Ericaceae]
• Melilota Medikus, 1787 (uncertain)
• Melima Por, 1964
• Meliola E.M. Fries, 1825
• Meliosma Blume, 1823
• Melipona Illiger, 1806
• Melisa Walker, 1854
• Melisia Lombardini, 1944
• Melispa Weise, 1897 accepted as Callispa Baly, 1858
• Melissa Linnaeus, 1753 [Family: Lamiaceae]
• Melissa Smith, 1854 (uncertain) [Family: Apidae]
• Melissa Strahl, 1861 accepted as Euxanthus Dana, 1851 [Family: Xanthidae]
• Melissoda Lepeletier, 1841 (unaccepted)
• Melisuga Agassiz, 1845 accepted as Mellisuga Brisson, 1760
• Melitoma Lepeletier & Serville, 1828
• Melitomma Haeckel, 1887 (uncertain)
• Melittoma accepted as Melittomma Murray, 1867
• Melivora Gray, 1847 accepted as Mellivora Storr, 1780
• Melosoma Bedel, 1892 accepted as Chrysomela Linnaeus, 1758
• Menosoma Ball, 1931
• Merosoma Balfour-Browne, 1939 accepted as Pelosoma Mulsant, 1844
• Mesosoma Otto, 1821 (uncertain) [Family: Crustacea (awaiting allocation)]
• Mesosoma Weed, 1892 accepted as Eumesosoma Cokendolpher, 1980 [Family: Sclerosomatidae]
• Molosoma Say, 1831 accepted as Osorius Guérin-Méneville, 1829
• Molosoma Say, 1834 accepted as Osorius Guérin-Méneville, 1829
• Mylosoma Eigenmann, 1915 accepted as Mylossoma Eigenmann & Kennedy, 1903