Unio crassidens Lamarck, 1819
Lister, 1685. Conch.: pl. 150, fig. 5.
Lamarck, 1819. Hist. Natur. Anim. sans Vert. 6: 71, sp. 3, var. a. [in part]
(misidentified reference to Unio crassidens Lamarck, 1819)

Quadrula (sec. Crenodonta) trapezoides — Simpson (1900), Simpson (1914)
Unio (s.s.) trapezoides — Call (1900)
Plectomerus trapezoides — Ortmann & Walker (1922)
Amblema (Plectomerus) dombeyana — Frierson (1927)
Plectomerus dombeyana — R.I. Johnson (1969), Oesch (1984)
Plectomerus dombeyanus — Howells et al. (1996), Parmalee & Bogan (1998), Williams et al. (2008)

Unio dombeyana Valenciennes, 1827
Valenciennes, 1827. Receuil Observ. Zool. 2(11-12): 227, pl. 53, figs. 1a-b.

Quadrula (sec. Crenodonta) trapezoides — Simpson (1900), Simpson (1914)
Plectomerus trapezoides — Ortmann & Walker (1922)
Amblema (Plectomerus) dombeyana — Frierson (1927), Haas (1969)
Amblema dombeyana — Thiele (1934)
Plectomerus dombeyanus — Haas (1969), Burch (1975), Gordon et al. (1979), R.I. Johnson (1980), Turgeon et al. (1988), ... FMCS (2021), Stodola et al. (2021), Hopper et al. (2023), Freeman et al. (2025), FMCS (2025)
Amblema dombeyanus — Davis & Fuller (1981)
Plectomerus dombeyana — Oesch (1984), Vidrine (1993)

Bariosta ponderosus Rafinesque, 1831
Rafinesque, 1831. Continuation: 2.
Rafinesque, 1864. [in] Binney & Tryon, reprint: 73.

Bariosta ponderosus — Simpson (1900), Simpson (1914)
Plectomerus trapezoides — Ortmann & Walker (1922)
Amblema (Plectomerus) dombeyana — Frierson (1927)
— Haas (1969)
Plectomerus dombeyanus — Burch (1975), Howells et al. (1996)
Plectomerus dombeyana — Oesch (1984)

Lasmigona ponderosa Rafinesque, 1831
Rafinesque, 1831. Continuation: 5.
Rafinesque, 1864. [in] Binney & Tryon, reprint: 79.

Unio interruptus Say, 1831
Say, 1831. Transylvania J. Med. Assoc. Sci. 4: 525.
Say, 1832. Amer. Conch. 4: pl. 33.
(homonym of Unio (Eurynia) solenoides var. interrupta Rafinesque, 1820)

Quadrula (sec. Crenodonta) trapezoides — Simpson (1900), Simpson (1914)
Plectomerus trapezoides — Ortmann & Walker (1922)
Amblema (Plectomerus) dombeyana — Frierson (1927)
Plectomerus dombeyanus — Haas (1969), Burch (1975), Howells et al. (1996), Parmalee & Bogan (1998), Williams et al. (2008)
Plectomerus dombeyana — Oesch (1984)

Unio trapezoides Lea, 1831
Lea, 1831. Trans. Amer. Phil. Soc. 4 [O. 1]: 69 [79], pl. 3, fig. 1.
Type(s): FIGURED SYNTYPE USNM_84103, Lake St. Joseph, Mis.

Quadrula (sec. Crenodonta) trapezoides — Simpson (1900), Simpson (1914)
Unio (s.s.) trapezoides — Call (1900)
Quadrula trapezoides — Ortmann (1909)
Crenodonta trapezoides — Ortmann (1912)
— de Gregorio (1914)
Plectomerus trapezoides — Ortmann & Walker (1922)
Amblema (Plectomerus) dombeyana — Frierson (1927)
Plectomerus dombeyanus — Haas (1969), Burch (1975), R.I. Johnson (1980), Howells et al. (1996), Parmalee & Bogan (1998), Williams et al. (2008), Williams et al. (2014), Graf & Cummings (2021)
Plectomerus dombeyana — Oesch (1984), Vidrine (1993)

Unio dombeiana Ferussac, 1835
‘Valenciennes’ of Authors.
Ferussac, 1835. Mag. Zool. 5(59-60): 27, 33.
Hanley, 1843. Illustr. Descr. Cat. Rec. Bivalve Shells: 175.
(error for Unio dombeyana Valenciennes, 1827)

Quadrula trapezoides var. pentagonoides Frierson, 1902
Frierson, 1902. Nautilus 16(4): 39.
Frierson, 1927. Check List N. Amer. Naiades: 62 [as ‘A. (Plectomerus) dombeyana’].
(intro'd as intra-sp. of Unio trapezoides Lea, 1831)
Type(s): LECTOTYPE ANSP_128928 (by R.I. Johnson, 1972: 147), Lake Charles, La.

Quadrula (sec. Crenodonta) trapezoides var. pentagonoides — Simpson (1914)
Amblema (Plectomerus) dombeyana — Frierson (1927)
Plectomerus dombeyanus — Haas (1969), Parmalee & Bogan (1998)

Complanaria trapezius Agassiz, 1852
Agassiz, 1852. Arch. Naturg. 18(1): 49.
(error for Unio trapezoides Lea, 1831)