Phylum: Euglenophyta   Family: Phacaceae

Phacus pleuronectes (O.F. Müller) Nitzsch ex Dujardin

Thought to be widespread in ditches, pools and bogs which are slightly acidic, but not common

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles