Phylum: Charophyta   Family: Desmidiaceae

Tetmemorus brebissonii  J. Ralfs 1848

First described and illustrated by Ralf (1848: 145, pl. 24: 1). This nominate variety occupies a less acidic, mesotrophic, habitat than some of the other varieties. The cell-wall is covered in pores which are arranged in longitudinal rows.
Cell dimensions: L: 150-240 µm; B: 25-48 µm; Is: 22-32 µm; L/B: 4.0-5.0.
West & West (1904: 216, pl. 32; 1-2) make an interesting observation: “This species is by no means common, and we never find it in any quantity except in permanent bogs and at the margins of lakes. It would appear that British specimens are larger than those found in many parts of continental Europe.” This is still the situation in the Outer Hebrides.

References: 
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland.
Ralfs, J. (1848) The British Desmidieae.
West, W. & West, G.S. (1904) A Monograph of the British Desmidiaceae, Volume 1.