Phylum: Chlorophyta   Family: Scenedesmaceae

Coelastrum verrucosum (P.F. Reinsch) P.F. Reinsch 1875

First described and illustrated by Reinsch (1875: 79, pl. 13: 8) as Sphaerastrum verrucosum. In the same year (Reinsch 1875: 104) transferred it to the current genus. Some authors have synonymised this species with C. sphaericum but the general consensus is that the cells are too distinct to warrant such a move.
Coenobia broadly spherical, usually 4, 8, & 16. Cell diameters: 10-24 µm.
Most British records are from Scotland but it would appear to be general scarce. Found in loch-margins and with plankton.

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition). The Freshwater Algal Flora of the British Isles.
Reinsch, P.F. (1875). Contributiones ad algologiam et fungologiam. Vol. 1.