Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subcoliferum R. Grönblad 1920

The sinus is narrowly open at the apex then opening widely. Semicells are transversely subelliptic with the broadest part below the median line. The cells are relatively thick-walled with the rounded lateral angles exhibiting some extra thickening. The cell-wall is covered in medium pores. Chloroplast is axile with a single pyrenoid.
Cell dimensions: L: 35-37.2 µm, B: 27.2-28.9 µm, Is: 8.2-9.1 µm; Th: c.20.4-21.6 µm; L/B:1.23-1.35.
A seemingly rare species found in mesotrophic waters. The two collections from the Outer Hebrides, as of 2025, have come from a shallow, silty, loch-margin, and from abandoned peat-cuttings.

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