Phylum: Charophyta   Family: Desmidiaceae

Xanthidium bifidum (Brébisson) Deflandre

This species had a name-change in 1996 to Octacanthium bifidum, but as the recording platforms have not caught up, I will leave it here for now. Found in shallow lochs and pools in Scotland. Not thought to be scarce but possibly overlooked being rather small

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. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
Kouwets, F.A.C. (1999) A check-list of desmids (Chlorophyta, Zygnemaphyceae) of France