Diplodon rotundus Wagner, 1827
Spix in Wagner, 1827. Test. Fluv. Brasil.: 34, pl. 26, figs. 3-4.

Diplodon (Cyclomya s.s.) rotundus — Simpson (1900), Simpson (1914)
Diplodon rotundus — Ihering (1910), Bonetto (1962), Graf & Cummings (2006), Pereira et al. (2014), Mansur et al. (2020), Graf & Cummings (2021), Torres et al. (2024)
Diplodon (s.s.) rotundus — Ortmann (1921), Rumi et al. (2008)
Diplodon (Cyclomya) rhombeus — Haas (1931)
Diplodon (Rhipidodonta) rotundus — Morretes (1949)
Diplodon rotundatus [sic] — Lucena (1951)
Diplodon (s.s.) rotundus rotundus — Bonetto (1965)
Diplodon rotundus rotundus — Parodiz (1968)
Diplodon (Rhipidodonta) rhombeus — Haas (1969)
Rhipidodonta rhombea — Simone (2006)

Unio quadrans Lea, 1860
Lea, 1860. Proc. Acad. Nat. Sci. 12: 306.
Lea, 1860. Jour. Acad. Nat. Sci. 4 [O. 8]: 360 [42], pl. 61, fig. 185.
Type(s): HOLOTYPE ANSP_125601, Texas.

Diplodon (s.s.) quadrans — Simpson (1900), Simpson (1914)
Diplodon (Cyclomya) fontainianus — Haas (1930), Haas (1931)
Diplodon rotundus rotundus — Parodiz (1968)
Diplodon (Rhipidodonta) fontainianus — Haas (1969)
Diplodon fontainianus — Simone (2006)

Unio rotundus Moricand, 1838
‘Wagn.’ Moricand, 1838. Mém. Soc. Phys. Hist. Nat. Genève 9(1): 63, pl. 4, figs. 12-14.
(reference to Diplodon rotundus Wagner, 1827)

Diplodon (Cyclomya s.s.) rotundus — Simpson (1900)

Unio quadraus B.H. Wright, 1888
‘Lea’ B.H. Wright, 1888. Check List N. Amer. Unionidae etc.: [5].
(error for Unio quadrans Lea, 1860)

Unio schenederi Ihering, 1893
‘Dunker’ Ihering, 1893. Arch. Naturg. 59(1): ??. [nomen nudum]

Diplodon rotundus rotundus — Parodiz (1968)

Diplodon rotundatus Lucena, 1951
‘Lamarck’ Lucena, 1951. Pap. Avuls. Dept. Zool. 10(3): 98.
(error for Diplodon rotundus Wagner, 1827)

Diplodon rotundatus — Simone (2006)