Phylum: Charophyta   Family: Desmidiaceae

Cosmarium ornatum J. Ralfs 1848

Semicells subreniform giving the sinuses a dilate apex. Sides broadly rounded with the apex protruding and truncate. Cell-wall covered in small granules that are frequently bifurcate. The central ornamentation comprises usually four large granules with a ring of medium granules encircling, this manifests as a substantial protuberance in apical and side views.
Cell dimensions: L: 34.8-38.1 µm; B: 34.7-38.2 µm; Is: 10.9-14.2; Th: 22.6-23.4 µm; L/B: 0.95-1.03.
Widespread and common in the Outer Hebrides, especially in moorland bogs and disused peat-cuttings.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
West, W. & West, G.S. (1908). A Monograph of the British Desmidiaceae, Volume 3.