Phylum: Charophyta Family: Desmidiaceae
Cosmarium ralfsii Brébisson ex Ralfs
An acidophile of moorland pools and bogs, especially with Sphagnum. In the Wests' time it was reported as widespread but I haven't found this to be the case now in the Outer Hebrides
References:
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2