Venericardia nodifera (FOSSIL) Kellum, 1926 † USA, North Carolina, Onslow
Venericardia nodosa (FOSSIL) (Dufour, 1881 †) France, Brittany25 mm
Megacardita nodulosa (J.B.P.A. Lamarck, 1819) Australia, Broome47 mm
Cardita northcrofti (FOSSIL) J. Marwick, 1928 †
Cyclocardia novangliae (E.S. Morse, 1869) Massachusetts, Nantucket
Coripia nuculoides (K.H. Barnard, 1964)
Fasciculicardia nuntia (FOSSIL) (J. Marwick, 1928 †) Canada, Quebec, Anticosti Island
Cardiocardita obesa R. von Cosel, 1995 Guinea Bissau17,3 mm
Gujocardita obesa (FOSSIL) Y. Fang, 1987 † China, Hunan, Chenzhou
Gujocardita oblonga (FOSSIL) Y. Fang, 1987 † China, Hunan, Chenzhou
Cyclocardia occidentalis (FOSSIL) (T.A. Conrad, 1855 †)
Cyclocardia ochotica (FOSSIL) (Slodkewitsch, 1936 †) Western Kamchatka
Venericardia olga (FOSSIL) W.C. Mansfield, 1939 † Florida50 mm
Megacardita ommaensis (FOSSIL) K. Ogasawara, 1977 † Japan, Ishikawa24 mm
Pleuromeris onerata (FOSSIL) (G.P. Deshayes, 1858 †) France, Paris Basin8 mm
Venericardia onerata (FOSSIL) (G.P. Deshayes †) France, Brittany5 mm
Venericardia oppenheimi (FOSSIL) A.E.M. Cossmann, 1904 † France, Brittany10 mm
Cyclocardia orbica (FOSSIL) M. Yokoyama, 1925 † Japan, Fukushima, Iwaki
Cyclocardia orbicularis (FOSSIL) (E. Forbes, 1846 †) Belgium20 mm
Cyclocardia orbicularis chamaeformis (FOSSIL) (J. de C. Sowerby,1825 †) Belgium
Cyclocardia orbicularis paucicostata (FOSSIL) (A. Krause, 1885 †) Germany, Rheinland-Pfalz8 mm
Cyclocardia orientalis (FOSSIL) L. Krishtofovich, 1984 † Western Kamchatka
Cyclocardia ornata (FOSSIL) (G.P. Deshayes, 1858 †) France, Paris Basin10 mm
Venericardia ornata (FOSSIL) (G.P. Deshayes †) France, Brittany11 mm
Megacardita osawanoensis (FOSSIL) K. Tsuda, 1959 † Japan, Akita, Akita
Venericardia oswaldi (FOSSIL) Sokolov † Ukraine
Pleuromeris otamateaensis (FOSSIL) C.R. Laws, 1944 †
Cyclocardia otatsumei (FOSSIL) S. Uozumi, 1955 † Japan, Hokkaido, Utashinai
Cardites ovalis (L.A. Reeve, 1843) Malaysia
Cyclocardia ovata (Riabinina, 1952) Alaska
Cyclocardia ovata (Rjabinina, 1952) Russia, Sakhalin
Fenestricardita ovata (FOSSIL) Tashiro, 1976 † Japan, Amakusa-Shimoshima
Gujocardita oviformis (FOSSIL) Nakazawa & Newell, 1968 † Japan, Kyoto, Fukuchiyama
Cyclocardia ovraensis (FOSSIL) V.N. Sinelnikova, 1991 † Western Kamchatka
Cyclocardia oyamai (FOSSIL) A.I. Kafanov, K. Ogasawara& K. Amano, 1999 † Western Kamchatka