Phylum: Charophyta   Family: Desmidiaceae

Cosmarium quadrum P.M. Lundell 1871

A large taxon with sub-rectangular semicells, the lower part of the sides about parallel, upper part convergent to broadly rounded apical angle. Apices truncate and occasionally slightly retuse.
Cell dimensions: L: 71-80 µm; B: 67-70 µm; Is: 27-31.4 µm; Th: 39.40 µm; L/B: 1.06-1.17.
Infrequently recorded in slightly acidic to circumneutral waters. Found in mesotrophic moorland pools, abandoned peat-cuttings and ditches. West & West (1912: 20) note: "… the rarest of the conspersum-group in the British Isles, …"

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.