This taxon has broad, bluntly rounded ends which are weakly drawn out. The valve is broadly laceolate. The raphe is filiform. The proximal raphe ends are thin, short hooks. The axial area is narrow and a central area is variously developed. Usually expressed as a diagonal region of poorly developed punctae, the central area sometimes appears to be lacking. The striae are oblique to the raphe and valve margin. The submarginal canal is parallel to the valve margin. There are very distinct punctae (Krammer and Lange-Bertalot 1986). This taxon is occasionally found in collections from all of the Great Lakes. Specimens illustrated are from Lake Superior (E.F. Stoermer collection).
Lower Lunz Lake, Austria
BRM NE 1/3 (Hustedt Collection, Lunzer Unter See, Finder 622.4)
This taxon is found in lake sediments, usually in deep water, or in shaded microhabitats in shallow water bodies. Krammer and Lange-Bertalot 1986 considered it to most likely be a subfossil, but Hamilton et al. 1996 have found it widely distributed in shallow Arctic ponds, and we have observed it in bottom sediments from several modern lakes in central North America as well as in post-Pleistocene lake sediments.