Unio declivis Say, 1831
Say, 1831. Transylvania J. Med. Assoc. Sci. 4: 527.
Say, 1832. Amer. Conch. 4: pl. 35.
Type(s): SYNTYPES ANSP_41698, Louisiana.

Unio (sec. Uniomerus) tetralasmus var. declivis — Simpson (1900), Simpson (1914)
Unio (s.s.) tetralasmus — Call (1900)
Unio declivis — de Gregorio (1914)
Elliptio (Uniomerus) declivis — Frierson (1927)
Uniomerus obesus — Clench & Turner (1956)
Uniomerus tetralasmus — Haas (1969), R.I. Johnson (1970), R.I. Johnson (1972), Burch (1975), R.I. Johnson (1999)
Uniomerus declivis — Davis (1983), Davis (1984), Turgeon et al. (1988), Howells et al. (1996), Parmalee & Bogan (1998), ... FMCS (2021), Neemuchwala et al. (2023), Hopper et al. (2023), FMCS (2025), Campbell & Lydeard (2026)
Uniomerus declivus [sic] — Williams et al. (1993), Vidrine (1993), Campbell et al. (2005), Inoue et al. (2018), Burlakova et al. (2019)
U. declivis — Marshall et al. (2018)

Unio geometricus Lea, 1834
Lea, 1834. Trans. Amer. Phil. Soc. 5 [O. 1]: 38 [150], pl. 4, fig. 10.
Type(s): HOLOTYPE USNM_85712, Bayou Teche, Louisiana.

Unio (sec. Uniomerus) tetralasmus var. camptodon — Simpson (1900), Simpson (1914)
Unio (s.s.) tetralasmus — Call (1900)
Unio declivis — de Gregorio (1914)
Uniomerus tetralasmus comptodon [sic] — Utterback (1915)
Elliptio (Uniomerus) declivis — Frierson (1927)
Uniomerus tetralasmus — Haas (1969), R.I. Johnson (1970), R.I. Johnson (1972), Burch (1975), Williams et al. (2008)
Uniomerus declivis — Parmalee & Bogan (1998)

Unio excultus Conrad, 1838
Conrad, 1838. Monogr. Fam. Unionidae 2(11): 99, pl. 55, fig. 1.
Conrad, 1853. Proc. Acad. Nat. Sci. 6: 249.

Unio (sec. Uniomerus) tetralasmus — Simpson (1900), Simpson (1914)
Unio (s.s.) tetralasmus — Call (1900)
Elliptio (Uniomerus) tetralasmus — Frierson (1927)
Uniomerus tetralasmus — Haas (1969), R.I. Johnson (1970), R.I. Johnson (1972), Burch (1975), Parmalee & Bogan (1998), Williams et al. (2008), IUCN (2012), Williams et al. (2014)
Uniomerus excultus — Davis (1983), Davis (1984), Turgeon et al. (1988), Williams et al. (1993), ITIS (2012)
Uniomerus declivis — Turgeon et al. (1998), Graf & Cummings (2007)

Uniomerus declivus Williams et al., 1993
‘Say’ of Authors.
Williams et al., 1993. Fisheries 18(9): 14.
Vidrine, 1993. Histr. Distr. Freshw. Mussels LA: 86.
Campbell et al., 2005. Invert. Biol. 124(2): 155.
Inoue et al., 2018. Invert. Syst. 32: Table S2.
Burlakova et al., 2019. Malacologia 62(2): 351.
(error for Unio declivis Say, 1831)

Margaron (Unio) declivis Lea, 1852
‘Say’ Lea, 1852. Synopsis Fam. Naiades: 33.
(reference to Unio declivis Say, 1831)

Unio (sec. Uniomerus) tetralasmus var. declivis — Simpson (1900)

Elliptio tetralasmus manubius Frierson, 1927
‘Gould’ Frierson, 1927. Check List N. Amer. Naiades: 34.
(misidentified reference to Unio manubius Gould, 1855)

Uniomerus declivis — Howells et al. (1996)