This species has linear valve, swollen in the middle portion; ends rounded, usually somewhat swollen, often almost as wide as the median portion of the valve. . Willam Smith gave the name Pinnularia acrosphaeria to this taxon. Rabenhorst, a few months later in 1853, made the combonation Pinnularia acrosphaeria for Brebisson's Frustulia acrosphaeria which is not this taxon. Dr. Willam Stearns of the British Museum has ascertained that volume one of William Smith's A Synopsis of the British Diatomaceae was published in 1853 before Rabenhorst's Die Susswasser-Diatomaceen (Bacillarien) (Patrick and Reimer 1966).