Phylum: Charophyta   Family: Desmidiaceae

Xanthidium fasciculatum J. Ralfs 1848

A medium-sized cell with the sinus closed for the most part and with a dilated extremity. Semicells angular-reniform with six equidistant paired spines around the margin. Apex about truncate, the central protuberance consists of several granules in a circular disposition. Occasionally, a granule can be observed at the basal angles. This used to be a defining character of the variety oronense, but Coesel & Meesters (2023: 194) have now incorporated that variety with the nominate as they consider it a taxonomically irrelevant feature, although they haven’t officially synonymised it. I fully agree with this move.
Cell dimensions: L: 46-51 µm; B: 43-47 µm; Is: 16-17 µm; Sp: 8-13 µm; Overall LxB: 60-73 x 58-67 µm.
West & West (1912: 75) found it a rare desmid. The Outer Hebridean finds have mainly come from acidic shallow lochs and lochans, but rarely recorded.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023. second edition) Desmids of the Lowlands.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.