Phylum: Charophyta   Family: Desmidiaceae

Cosmarium regnesi var. tritum  West

Differs mainly from the nominate variety by have a 'V-shaped' sinus. The habitat is shallow moorland pools and bogs which are slightly acidic.

References: 
West, W. & West, G.S. (1908) A Monograph of the British Desmidiaceae, Volume 3