Phylum: Charophyta   Family: Desmidiaceae

Cosmarium amoenum J. Ralfs 1848

There is similarity with C. sphaeroideum West 1892 but that species is a little larger, especially in breadth giving a smaller L/B ratio.
Cell dimensions: L: 42-59 µm, B: 23-31 µm, Is: 15-17 µm; Th: 21-24 µm, L/B: 1.7-1.9.
An infrequently found species with the British population seemingly confined to the granitic regions of Scotland and Ireland. An acidophile largely confined to moorland bogs especially with Sphagnum.

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