Phylum: Charophyta   Family: Desmidiaceae

Cosmarium anceps P. Lundell 1871

West & West (1908: 48) make no mention of scarcity and give many references to it in Britain. They note: “C. anceps is nearly allied to C. decedens, from which it can be distinguished by its somewhat smaller size, its narrower apices with less prominent apical angles, and by the straighter (less retuse) sides of the semicells.”
Cell dimensions (2): L: 28.9-33.3 µm, B: 15.8-19 µm, Is: 10.9-14.2 µm; Th: 12.9-15.7 µm, L/B: 1.76-1.83.
A rare species even in its preferred habitat of atmophytic substrates and ephemeral pools.
The two specimens found here have come from: 1. Ephemeral flood water and 2. Wet moss on dripping rocks, both subject to desiccation.

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