Phylum: Charophyta   Family: Desmidiaceae

Xanthidium antilopaeum F.T. Kützing 1849

A variable species that has spawned numerous infraspecific taxa. Typical semicells are subelliptic to hexagonal. The sinus can be closed or partly open depending on the basal shape of the semicells. Semicells have four paired spines at the apical and lateral angles. The central scrobiculation varies considerably from ephemeral to quite pronounced. West & West (1912, pl. 108: 10-17) illustrate 8 types.
Cell dimensions: L: 51-77 µm; B: 44-64 µm; Is: 15-27 µm; Sp: 12-15 µm; Overall LxB: 65-95 x 67-92 µm.
A common desmid found 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.