Phylum: Charophyta Family: Desmidiaceae
Cosmarium contractum var. notatum (Raciborski) Playfair 1917
This genus is very variable and has spawned several varieties. The parameters have been stretched over time, which has lead to much confusion. Kouwets (in manuscript) is attempting to sort it out, both historically and in light of more recent discoveries. This species has central lenticular cell-wall thickening, but it's only visible in side and apical views.
Playfair, G.J. (1917) Census of New South Wales freshwater algae. In: A census of New South Wales plants: "With supplements to follow on vascular cryptogams by various specialists." (edited by Maiden, J.H. & Betche, E.)
Raciborski (1892) Desmidyja zebrane przez Dr. E. Ciastonia, w podrózy na okolo ziemi
Kouwets, F.A.C. (in manuscript) European Flora of the Desmid Genus Cosmarium