Phylum: Charophyta   Family: Desmidiaceae

Cosmarium basiornatum (R.L. Grönblad) P.F.M. Coesel 1998

Semicells in face view are narrowly trapeziform, 5-undulate on each side. Apices truncate and 4-undulate. It needs to be compared with the similar C. davidsonii Roy & Bisset 1894, which it was once associated with.
Cell dimensions (3): L: 38.3-40.1 µm; B: 27.3-28.8 µm; Is: 14.5-15.9 µm; Th: 19.8-20.3; L/B: 1.38-1.41.
A seemingly scarce desmid throughout Europe. The Outer Hebridean finds have all come from shallow, semi-permanent rainwater pools.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.