Unio semigranosus Philippi, 1843
von dem Busch in Philippi, 1843. Abbild. Beschr. Conch. 1: 19, pl. 1, figs. 1-3.
Type(s): PARATYPES MCZ_152861, near Tampico, Mexico.

Unio (sec. Elliptio) semigranosus — Simpson (1900), Simpson (1914)
Unio (Psoronaias) semigranosus — Martens (1900)
Quadrula semigranosa — Pilsbry (1910)
Psoronaias semigranosus — Frierson (1917), Frierson (1927), Haas (1930), Goodrich & van der Schalie (1937)
Psoronaias semigranosa — Haas (1929), Graf & Cummings (2007), Bogan (2010), Pfeiffer et al. (2019), Pfeiffer et al. (2019), Inoue et al. (2020), Smith et al. (2020), Graf & Cummings (2021), Czaja et al. (2023), Freeman et al. (2025)
Psoronaias semigranosa semigranosa — Haas (1969)

Unio crocodilorum Morelet, 1849
Morelet, 1849. Test. Nov. 1: 28.
Type(s): SYNTYPE BMNH_1893-2-4-2030, River Usumacinta, Central America.

Unio (sec. Elliptio) crocodilarum [sic] — Simpson (1900), Simpson (1914)
Unio (Psoronaias) crocodilorum — Martens (1900)
Psoronaias crocodilorum — Frierson (1917), Frierson (1927), Haas (1930), Haas (1969), Graf & Cummings (2007), Bogan (2010)
Psoronaias crocodilarum [sic] — Haas (1929)
Psoronaias semigranosus — Goodrich & van der Schalie (1937)
Psoronaias semigranosa — Graf & Cummings (2021)

Unio testudineus Morelet, 1849
Morelet, 1849. Test. Nov. 1: 28.
Type(s): HOLOTYPE BMNH_94-3-22-1, flumen Usumacinta, Guatemala.

Unio (sec. Elliptio) testudineus — Simpson (1900), Simpson (1914)
Unio (Psoronaias) semigranosus var. testudineus — Martens (1900)
Psoronaias semigranosus — Frierson (1927)
Psoronaias testudinea — Haas (1929), Haas (1969)
Psoronaias testudineus — Haas (1930)
Psoronaias testudinarea [sic] — Bogan (2010)

Unio morini Morelet, 1851
Morelet, 1851. Test. Nov. 2: 25.
Type(s): HOLOTYPE BMNH_93-2-4-2026, Rio Usumacinta, Guatemala.

Unio (sec. Elliptio) morini — Simpson (1900), Simpson (1914)
Unio (Psoronaias) morini — Martens (1900)
Psoronaias morini — Frierson (1927), Haas (1929), Haas (1930), Haas (1969), Graf & Cummings (2007), Bogan (2010)
Psoronaias semigranosus — Goodrich & van der Schalie (1937)
Psoronaias semigranosa — Graf & Cummings (2021)

Unio psoricus Morelet, 1851
Morelet, 1851. Test. Nov. 2: 25.
Type(s): HOLOTYPE BMNH_93-2-4-2033, Rio Usumacinta, Tabasco.

Unio (sec. Elliptio) psoricus — Simpson (1900), Simpson (1914)
Unio (Psoronaias) psoricus — Martens (1900)
Psoronaias psoricus — Frierson (1917), Haas (1930), Thiele (1934)
Psoronaias semigranosus-psoricus — Frierson (1927)
Psoronaias psorica — Haas (1929), Haas (1969), Haas (1969), Bogan (2010)
Psoronaias semigranosus — Goodrich & van der Schalie (1937)
Psoronaias semigranosa — Graf & Cummings (2007), Pfeiffer et al. (2019), Graf & Cummings (2021)

Unio corium Reeve, 1864
Reeve, 1864. Conch. Icon. 16: pl. 10, sp. 39.
Type(s): HOLOTYPE BMNH_1965209, Chiapas, Mexico.

Unio (sec. Elliptio) corium — Simpson (1900), Simpson (1914)
Unio (Psoronaias) corium — Martens (1900)
Unio corium — Pilsbry (1910)
Psoronaias semigranosus-corium — Frierson (1927)
Psoronaias semigranosus — Haas (1930), Goodrich & van der Schalie (1937)
Psoronaias semigranosa corium — Haas (1969)

Unio crocodilorum var. B semipustulata Fischer & Crosse, 1894
Fischer & Crosse, 1894. Miss. Sci. Mexique, Rech. Zool. 2(16): 578, pl. 60, fig. 4.
(intro'd as intra-sp. of Unio crocodilorum Morelet, 1849)
Type(s): PARATYPES BMNH_1893-2-4-2032, River Usumacinta, Guatemala.

Unio (Psoronaias) crocodilorum — Martens (1900)
Psoronaias crocodilorum — Frierson (1927), Haas (1969)
Psoronaias crocodilarum [sic] — Haas (1929)

Unio crocodilorum var. G praestricta Fischer & Crosse, 1894
Fischer & Crosse, 1894. Miss. Sci. Mexique, Rech. Zool. 2(16): 578, pl. 60, fig. 5.
(intro'd as intra-sp. of Unio crocodilorum Morelet, 1849)
Type(s): SYNTYPES BMNH_1893-2-4-2031, River Usumacinta, Guatemala.

Unio (Psoronaias) crocodilorum — Martens (1900)
Psoronaias crocodilorum — Frierson (1927), Haas (1969)

Quadrula rudis Simpson, 1900
Simpson, 1900. Proc. Acad. Nat. Sci. 52: 82, pl. 3, fig. 2.
Simpson, 1914. Descr. Cat. Naiades: 910.
Type(s): HOLOTYPE (MONOTYPY) USNM_84210, Rio Taxtunilha, (tributary to the Rio de la Pasion), Guatemala.

— Simpson (1900)
Quadrula rudis — Simpson (1900)
Quadrula (Rotundaria) rudis — Simpson (1914)
Psoronaias rudis — Frierson (1927)
Rotundaria rudis — Haas (1929)
Amblema (Psorula) rudis — Haas (1930)
Amblema (sec. Psorula) rudis — Thiele (1934)
Psoronaias semigranosus — Goodrich & van der Schalie (1937)
Psorula rudis — Haas (1969), Graf & Cummings (2007), Bogan (2010), Pfeiffer et al. (2019), Inoue et al. (2020), Freeman et al. (2025)
Psoronaias semigranosa — Graf & Cummings (2021)

Unio crocodilarum Simpson, 1900
‘Morelet’ of Authors.
Simpson, 1900. Proc. U.S. Nat. Mus. 22: 702.
Simpson, 1914. Descr. Cat. Naiades: 591.
Haas, 1929. Senckenbergiana 11: 332.
(error for Unio crocodilorum Morelet, 1849)

Unio crocolilorum Lea, 1852
‘Morelet’ Lea, 1852. Synopsis Fam. Naiades: 39.
(error for Unio crocodilorum Morelet, 1849)

Unio testidineus Lea, 1852
‘Morelet’ Lea, 1852. Synopsis Fam. Naiades: 40.
(error for Unio testudineus Morelet, 1849)

Unio pliciferus Reeve, 1864
‘Lea’ Reeve, 1864. Conch. Icon. 16: pl. 10, sp. 37; errata [changed to ‘U. crocodilorum Morelet’].
(misidentified reference to Unio pliciferus Lea, 1838; error for Unio crocodilorum Morelet, 1849)

Unio (Psoronaias) crocodilorum — Martens (1900)
Unio (sec. Elliptio) crocodilarum [sic] — Simpson (1900), Simpson (1914)
Psoronaias crocodilorum — Frierson (1927)
— Haas (1969)

Unio semigranosus Reeve, 1864
‘Philippi’ Reeve, 1864. Conch. Icon. 16: pl. 10, sp. 36; errata.
(reference to Unio semigranosus Philippi, 1843)
Type(s): FIGURED SPECIMEN BMNH_196496, Mexico.

Unio (sec. Elliptio) testudineus — Simpson (1900), Simpson (1914)
Unio (Psoronaias) semigranosus var. testudineus — Martens (1900)

Psoronaias testudinarea Bogan, 2010
‘Morelet’ Bogan, 2010. FADA: [web].
(error for Unio testudineus Morelet, 1849)