Phylum: Charophyta   Family: Desmidiaceae

Cosmarium bioculatum J. Ralfs 1848 sensu F.A.C. Kouwets 2011

This form had been previously listed and figured under C. cf bioculatum in Kouwets (2001: 35). The open, acute-angled sinus is a key character. The author has kindly identified my cells for me. Because of the taxonomic confusion regarding Cosmarium bioculatum J. Ralfs 1848, Kouwets proposes to rename this taxon Cosmarium bioculatiforme.
Kouwet’s Cell dimensions: L: 11-19 µm, B: 10.5-21.5 µm, Is. 3.5-4.5 µm; Th. 7-9 µm L/B: 0.84-1.13. (Mine fall within these.)
The current finds are from a shallow pool rich in vegetation with a neutral pH. Because of the uncertainty over identification its status in the Outer Hebrides is unknown.

References: 
Kouwets, F.A.C. (2001). Contributions to the knowledge of the French desmid flora 3. New and rare taxa from the regions of Dordogne and Limousin.