Venericardia nodifera (FOSSIL) Kellum, 1926 †
Venericardia nodosa (FOSSIL) (Dufour, 1881 †)
Megacardita nodulosa (J.B.P.A. Lamarck, 1819)
Cardita northcrofti (FOSSIL) J. Marwick, 1928 †
Cyclocardia novangliae (E.S. Morse, 1869)
Coripia nuculoides (K.H. Barnard, 1964)
Fasciculicardia nuntia (FOSSIL) (J. Marwick, 1928 †)
Cardiocardita obesa R. von Cosel, 1995
Gujocardita obesa (FOSSIL) Y. Fang, 1987 †
Gujocardita oblonga (FOSSIL) Y. Fang, 1987 †
Cyclocardia occidentalis (FOSSIL) (T.A. Conrad, 1855 †)
Cyclocardia ochotica (FOSSIL) (Slodkewitsch, 1936 †)
Venericardia olga (FOSSIL) W.C. Mansfield, 1939 †
Megacardita ommaensis (FOSSIL) K. Ogasawara, 1977 †
Pleuromeris onerata (FOSSIL) (G.P. Deshayes, 1858 †)
Venericardia onerata (FOSSIL) (G.P. Deshayes †)
Venericardia oppenheimi (FOSSIL) A.E.M. Cossmann, 1904 †
Cyclocardia orbica (FOSSIL) M. Yokoyama, 1925 †
Cyclocardia orbicularis (FOSSIL) (E. Forbes, 1846 †)
Cyclocardia orbicularis chamaeformis (FOSSIL) (J. de C. Sowerby,1825 †)
Cyclocardia orbicularis paucicostata (FOSSIL) (A. Krause, 1885 †)
Cyclocardia orientalis (FOSSIL) L. Krishtofovich, 1984 †
Cyclocardia ornata (FOSSIL) (G.P. Deshayes, 1858 †)
Venericardia ornata (FOSSIL) (G.P. Deshayes †)
Megacardita osawanoensis (FOSSIL) K. Tsuda, 1959 †
Venericardia oswaldi (FOSSIL) Sokolov †
Pleuromeris otamateaensis (FOSSIL) C.R. Laws, 1944 †
Cyclocardia otatsumei (FOSSIL) S. Uozumi, 1955 †
Cardites ovalis (L.A. Reeve, 1843)
Cyclocardia ovata (Riabinina, 1952)
Cyclocardia ovata (Rjabinina, 1952)
Fenestricardita ovata (FOSSIL) Tashiro, 1976 †
Gujocardita oviformis (FOSSIL) Nakazawa & Newell, 1968 †
Cyclocardia ovraensis (FOSSIL) V.N. Sinelnikova, 1991 †
Cyclocardia oyamai (FOSSIL) A.I. Kafanov, K. Ogasawara& K. Amano, 1999 †