Abruptolopha abrupta (FOSSIL) (d'Orbigny 1842) †
Liostrea acuminata (FOSSIL) (Sowerby, 1816 †)
Crassostrea afra (FOSSIL) Bohm, 1926 †
Ostrea agnevoensis (FOSSIL) L. Krishtofovich, 1957 ex Lautenschläger MS †
Crassostrea alabamiensis (FOSSIL) (Lea, 1833 †)
Ostrea albertensis (FOSSIL) H.D. Russell & Landes,1937 †
Ostrea algoensis G.B. II Sowerby, 1871
Lopha alternans (FOSSIL) Cragin, 1893 †
Cubitostrea alvarezii (FOSSIL) (A.V.M.D. D'Orbigny,1842 †)
Ostrea amorpha E. Forbes, 1846
Ostrea angasi Sowerby, 1846
Myrakeena angelica (A. de Rochebrune, 1895)
Dendostrea angermanni (FOSSIL) L.G. Hertlein, 1927 †
Crassostrea angulata (J.B.P.A. Lamarck, 1819)
Ostrea angusta (FOSSIL) G.P. Deshayes, 1824 †
Ostrea anomialis (FOSSIL) J.B.P.A. Lamarck, 1819 †
Ostrea anomioides (FOSSIL) F.B. Meek in Stanton,1893 †
Ostrea antarctica (FOSSIL) Zinsmeister, 1984 †
Striostrea appressa (FOSSIL) (W.M. Gabb, 1869 †)
Lopha aquitanica (FOSSIL) (C. Mayer, 1858 †)
Liostrea arabica (FOSSIL) Stefanini, 1925 †
Ostrea arcula (FOSSIL) J. Marwick, 1928 †
Ostrea arenicola (FOSSIL) R. Tate, 1886 †
Crassostrea ariakensis (T. Fujita in Wakiya,1929)
Ostrea arrosis (FOSSIL) T.H. Aldrich, 1904 †
Crassostrea ashleyi (FOSSIL) L.G. Hertlein, 1943 †
Ostrea atherstonei R.B. Newton, 1913
Ostrea atwoodii (FOSSIL) W.M. Gabb, 1866 †
Pustulostrea australis (J.B.P.A. Lamarck, 1819)
Ferganea bashibulakeensis (FOSSIL) Lan & Wei 1995 †
Ostrea bataviana (FOSSIL) Martin, 1909 †
Crassostrea belcheri (G.B. II Sowerby, 1871)
Hyotissocameleo bellaplicata (FOSSIL) (Shumard 1860) †
Bellostrea bellovacina (FOSSIL) (J.B.P.A. Lamarck,1806 †)
Ostrea beloiti (FOSSIL) Logan, 1899 †