Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subquadrans W. & G.S. West 1905

A small cell with the sinuses closed for the most part, basal angle rounded, sides convex and converging, blending smoothly with the slightly convex apex. Chloroplast axile with one pyrenoid, (reports of two pyrenoids per semicell seem highly unlikely).
Cell dimensions: L: 24.6-27 µm, B: 26.9-29 µm, Is: 8.8-10.4 µm; Th: 14.6 µm, L/B: 1.91-0.97.
An acidophile found in moorland pools and bogs. Its status in the Outer Hebrides is unclear, but as of 2025 it has rarely been recorded.

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