Five fossil species of Rhizosolenia are known only from the distal parts of the valve. The resemblance of these tubular structures to the proboscis of the modern genus Proboscia Sundström, together with the possession of spinulae and a longitudinal slit, suggests that these species should be transferred to Proboscia. The five new combinations made are P. cretacea (Cretaceous to Paleocene), P. interposita (Oligocene), P. praebarboi (Miocene), P. barboi (Miocene to Quaternary), and P. curvirostris (Quaternary). Records of “Rhizosolenia alata” from the fossil record appear to be erroneous. On the basis of these and modern species, the description of the genus is augmented.