Phylum: Charophyta   Family: Desmidiaceae

Cosmarium contractum var. ellipsoideum (Elfving) West & G.S. West

Can be quite common in nutrient-poor lochs and bogs of the north-west of Scotland

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. (1905) A Monograph of the British Desmidiaceae, Volume 2