Phylum: Charophyta   Family: Desmidiacea

Xanthidium hebridarum (W. & G.S. West) P.F.M. Coesel & K.J. Meesters 2023

The main distinguishing feature of this taxon is six spines per semicell. Two are lateral and the third at the apical angle. (However, the apical spine is often found paired.) This configuration gives a less typical subelliptic to hexagonal shapes as found in, say, Xanthidium antilopaeum. The sinus can be closed or partly open depending on the basal shape of the semicells. The central area consists of a small mamillate protuberance encircled by small scrobiculations.
Cell dimensions: L: 49-55 µm; B: 43-53 µm; Is: 14-17 µm; Sp: 6-14 µm; Th: c.31 µm; Overall LxB: 59-68 x 68-78 µm.
An infrequently found desmid in acidic waters such as loch-margins and moorland pools.

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.