Phylum: Charophyta   Family: Desmidiaceae

Xanthidium robinsonianum W. Archer 1880

First described by Archer (1880: 114, 116), at an exhibition of the Dublin Microscopical Club, where he found it in Counties Armagh and Donegal. Shortly after a Mr. Crowe found it at Glengariffe, and County Kildare, where he also found a zygospore. Most later records, beyond Ireland, are from Shetland and Sutherland.
Overall cell dimensions: L: 25-29 µm; B: 25-29 µm; Is: 7-9 µm.
Zygospore: minus projections: 26 µm; overall: 47 µm.
A generally rare desmid that can be locally common in peaty margins of lochs and abandoned peat-cuttings.

References: 
Archer, W. (1880) Proceedings of Societies: Dublin Microscopical Club.
John, D.M. & Williamson, D.B. (2009). A Practical Guide to the Desmids of the West of Ireland.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.