U. bigbyensisLea, ’41.U. estabrookianusLea, ’45.U. fassinansLea, ’68.Pleurobema fassinans rhomboideaSimpson, ’00.
The most frequent form isfassinans rhomboidea(topotypes examined), with rays poorly developed.U. bigbyensishas more distinct rays;U. estabrookianus(topotypes examined) is an old, overgrown form, without rays;U. fassinansis founded upon an individual (type examined, also topotypes), which is exceptionally elongated, without rays.