Phylum: Charophyta   Family: Desmidiaceae

Cosmarium quadratum Ralfs ex Ralfs

Widespread and common in upland peaty pools, bogs and disused peat-cuttings. The sides can be straight or retuse from a rounded basal angle

References: 
John, D.M. & Williamson, D.B. (2009). A Practical Guide to the Desmids of the West of Ireland
Coesel, P.F.M. & Meesters, K.J. (2007). Mesotaeniaceae and Desmidiaceae of the European Lowlands
West, W. & West, G.S (1908). A Monograph of the British Desmidiaceae, Volume 3