The figure of this month's MUSSELp Mussel of the Month is from Spix & Wagner's 19th century treatment of the freshwater Mollusca of Brazil. They actually favored two different names for the shell illustrated above: Unio caudatus and Diplodon furcatum! This potential confusion, however, is moot since the same species was described earlier by Schumacher under the name Prisodon obliquus.
Superfamily Etherioidea Deshayes, 1830
Family Hyriidae Swainson, 1840
Subfamily Hyriinae s.s.
Genus Prisodon Schumacher, 1817
Species Prisodon obliquus Schumacher, 1817
(+ Unio caudatus + Diplodon furcatum, Spix & Wager, 1827)