Phylum: Charophyta   Family: Desmidiaceae

Micrasterias crux-melitensis J. Ralfs 1848

An attractive cell with the sinuses and lobes well separated. The polar lobe extends beyond the adjacent lobes with the apices in the form of a saddle.
Cell dimensions (2): L: 114-128 µm; B: 109-123 µm; Is: 17.5-19.2 µm; L/B: 1.04-1.05.
West & West (1905: 116) note it as a rare species in Britain with no records for either the Inner or Outer Hebrides. However, Coesel & Meesters (2023: 104) note for the Netherlands: “Rather common in fen hollows and fen pits, …” The situation in the Outer Hebrides reflects the Wests comments in being rare, but also reflects the habitat in the Netherlands in being slightly alkaline.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
West, W. & West, G.S. (1905). A Monograph of the British Desmidiaceae, Volume 2.