Phylum: Charophyta Family: Desmidiaceae
Cosmarium bioculatum var. depressum (Schaarschmidt) Schmidle 1894
This variety (and, indeed, the species) is taxonomically confused. The original concept is of a cell about as long as broad with an L/B: ratio close to 1.00. It has a slightly open, parallel sinus. Found in slightly acidic, mesotrophic, waters. It would seem to be more common than the nominate variety.
References:
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium.
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles.
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2.
Croasdale, H. & Flint, E.A. (1988) Flora of New Zealand: Desmids, Volume 2.