Phylum: Charophyta   Family: Desmidiaceae

Xanthidium bifidum (L.A. de Brébisson) G. Deflandre 1929

A small cell with a narrowly to more widely open sinus from a rounded apex, lateral sides divergent and about straight but occasionally convex, truncate apical angle with two short spines, apex broadly truncate to markedly concave.
Cell dimensions: L: 12-13.5 µm; B: 11.5-12.2 µm; Is: 5.7-6 µm; Sp: 1-2.5 µm; Overall LxB: 14-16.5 x 14.5-16 µm.
Infrequently recorded in the Outer Hebrides possibly overlooked because of its small size. Found in circumneutral waters such as moorland pools and loch-margins.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024).Sieralgen in Drenthe.