Amphispongia oblonga Salter, 1861 is a Silurian problematic organism from Scotland originally described as a sponge. It forms the base of the lyssakid family Amphispongiidae Rauff, 1894. It has been suggested that the fossil may be an alga (Finks, 1967) which is now accepted, and Amphispongia is here redescribed as a dasycladacean alga. A new tribe Amphispongieae comprising Amphispongia Salter, 1861 and Anomaloides Ulrich, 1878 is erected Includes bibliographical references (p. 20-22) Amphispongia oblonga Salter, 1861 is a Silurian problematic organism from Scotland originally described as a sponge. It forms the base of the lyssakid family Amphispongiidae Rauff, 1894. It has been suggested that the fossil may be an alga (Finks, 1967) which is now accepted, and Amphispongia is here redescribed as a dasycladacean alga. A new tribe Amphispongieae comprising Amphispongia Salter, 1861 and Anomaloides Ulrich, 1878 is erected Fieldiana series has been published as Geological Series by Field Columbian Museum (1895-1909) and Field Museum of Natural History (1909-1943), and as Fieldiana: Geology by Chicago Natural History Museum (1945-1966) and Field Museum of Natural History (1966-)