Carychium nouleti (FOSSIL) J.R. Bourguignat, 1857 †
Leuconopsis novimundi (H.A. Pilsbry& J.T.L. McGinty, 1949)
Melampus nucleolus E.C. Von Martens, 1865
Cassidula nucleus (J.F. Gmelin, 1791)
Cassidula nucleus crassiuscula A. Mousson, 1869
Cassidula nucleus vitensis (A. Mousson, 1869)
Melampus nuxcastaneus J.T. Kuroda, 1949
Zospeum obesum (G.R. von Frauenfeld,1854)
Pedipes oblongus (C.F. Jickeli, 1874)
Ellobium obsoleta (FOSSIL) Phillips, 1829 †
Leuconopsis obsoleta (F.W. Hutton, 1873)
Carychium occidentale H.A. Pilsbry, 1891
Microtralia occidentalis (L. Pfeiffer, 1854)
Laemodonta octanfracta (I.H. Jonas, 1845)
Ellobium ogormani (FOSSIL) (A.E.M. Cossmann, 1923 †)
Melampus olivaceus P.P. Carpenter, 1857
Auriculastra oparica (H. Adams & A. Adams,1854)
Ellobium opportunatum A.A. Gould, 1859
Ophicardelus ornatus (A.E.J. Férussac, 1821)
Pedipes ovalis C.B. Adams, 1849
Ellobium ovatum (FOSSIL) (J.B.P.A. Lamarck,1804 †)
Tralia ovula (J.G. Bruguière, 1789)
Melampus ovuloides J.R.C. Quoy & J.P. Gaimard,1832
Microtralia ovulum (L. Pfeiffer, 1840)
Carychium pachychilus (FOSSIL) Sandberger, 1872 †
Pythia pachyodon H.A. Pilsbry & Y. Hirase,1908
Leuconopsis pacifica W.R.B. Oliver, 1915
Carychium paganettii F. Zimmermann, 1925
Auriculodes pallidum (G.B. II Sowerby, 1839)
Cassidula paludosa A. Garrett, 1872
Cassidula paludosa nigrobrunnea H.A. Pilsbry & Y. Hirase,1905
Tralia panamensis (C.B. Adams, 1852)
Pythia pantherina (A. Adams, 1851)
Melampus paranus (J.P.E. Morrison, 1951)
Marinula parva W.J. Swainson, 1856