Epioblasma obliquata (C.S. Rafinesque, 1820)
Radiatula occata (I. Lea, 1860)
Ptychobranchus occidentalis (T.A. Conrad, 1836)
Elliptio occulta (I. Lea, 1843)
Leptodea ochracea (T. Say, 1817)
Sinanodonta ogurae (J.T. Kuroda & T. Habe,1987)
Potamilus ohiensis C.S. Rafinesque, 1820
Solenaia oleivorus (P.M. Heude, 1877)
Palindonaia oligocenica (FOSSIL) R. Marquet, Lenaerts& Laporte, 2012 †
Parreysia olivacea B. Prashad, 1930
Obovaria olivaria C.S. Rafinesque, 1820
Radiatula olivaria (I. Lea, 1831)
Pseudodon omiensis H. von Heimburg, 1884
Barynaias opacata (J.C.H. Crosse& P.H. Fischer, 1893)
Anodonta oregonensis I. Lea, 1838
Nephronaias oregonensis (I. Lea, 1852)
Elongaria orientalis (Lea, 1840)
Lampsilis ornata T.A. Conrad, 1835
Villosa ortmanni (B. Walker, 1925)
Psoronaias ostreata (P.M.A. Morelet, 1849)
Dysnomia othcaloogensis (I. Lea, 1857)
Lampsilis ovata (T. Say, 1817)
Lampsilis ovata ventricosa D.W. Barnes, 1823
Acuticosta ovata (C.T. Simpson, 1900)
Pleurobema oviforme T.A. Conrad, 1834
Lanceolaria oxyrhyncha E.C. Von Martens, 1861
Fusconaia ozarkensis (R.E. Call, 1887)
Radiatula pachysoma (W.H. Benson, 1862)
Delphinonaias paludosa (P.M.A. Morelet, 1849)
Disconaias panacoensis (G. von dem Buschin R.A. Philippi, 1843)
Trapezoideus panhai Konopleva, Bolotov& Kondakov, 2017
Inversidens pantoensis (M. von Neumayr, 1899)
Schepmania parcesculpta (E.C. Von Martens, 1903)
Medionidus parvulus (I. Lea, 1860)
Toxolasma parvus (D.W. Barnes, 1823)