This species is a variety of dubium. It is only slightly different from dubium. The only difference is that the valve constricts slightly at the center. One other oddity about this taxon is occasionally a type occurs where the margins are flattened slightly halfway between the center and the ends. It closely follows dubium so the following information is from the genera dubium. The taxon usually has tapered sides and the valve is linear. The ends of the raphe valves are straight and the distal ends are for the most part indistinct. The striae for this taxon is radiate to parallel. It is best distinguished by the straight proximal ends of the raphe valve along with the shallow punta and the striae (Patrick and Reimer 1966).