Cochliopina minor (H.A. Pilsbry, 1920)
Tryonia minuscula (FOSSIL) W.M. Gabb, 1869 †
Ecpomastrum mirum F. Haas, 1957
Thalassobia moitessieri (J.R. Bourguignat, 1876)
Tryonia molinae R. Hershler, H.P. Liu& J.J. Landye, 2011
Aphaostracon monas (H.A. Pilsbry, 1899)
Tryonia monitorae R. Hershler, 1999
Heleobia montana (A. Doering, 1884)
Toxosoma multicarinatum (FOSSIL) Wesselingh, 2006 †
Littoridina nana Er. Marcus & Ev. Marcus,1963
Cochliopina navalis J.P.E. Morrison, 1946
Heleobia neveui (A.R.J.B. Bavay, 1904)
Emmericiella novimundi (H.A. Pilsbry, 1909)
Tryonia nuttalli (FOSSIL) Wesselingh, 2006 †
Tryonia oasiensis R. Hershler, H.P. Liu& J.J. Landye, 2011
Littoridina oblonga W.A. Biese, 1944
Littoridina obtusa W.A. Biese, 1944
Heleobia occidentalis (A. Doering, 1884)
Littoridina opachensis W.A. Biese, 1948
Littoridina orcutti (H.A. Pilsbry, 1928)
Aroapyrgus orizabensis (J.C.H. Crosse& P.H. Fischer, 1891)
Strombopoma ortoni (H.A. Pilsbry, 1924)
Dyris ortoni (FOSSIL) (W.M. Gabb, 1869 †)
Sioliella ovata (FOSSIL) Wesselingh, 2000 †
Toxosoma ovatum (FOSSIL) Wesselingh, 2006 †
Littoridina pachispira W.A. Biese, 1944
Aphaostracon pachynotus F.G. Thompson, 1968
Aroapyrgus panamensis (G.W. Tryon, 1863)
Zetekina panamensis (P. Bartsch, 1920)
Aroapyrgus panzosensis (B. Walker, 1919)
Littoridina parchappei (A.V.M.D. D'Orbigny,1835)
Heleobia parchappii (A.V.M.D. D'Orbigny,1835)
Pyrgophorus parvulus (L. Guilding, 1828)
Rhamphopoma parvum F. Haas, 1955
Aroapyrgus pasionensis (C. Goodrich& H. Van Der Schalie, 1937)