Pterocystis quadrata  Cavalier-Smith and Von der Heyden, 2007
  
Diagnosis: cells 10-20 µm. Radial spine-scales (3-5 µm) with broad axial rib tapering near the tip and base, distally strongly curved to one side, and offset from the centre to that same side making the scale much less bilaterally symmetrical than in other species and extending apically well beyond the lateral wings; wings unribbed, basally square in appearance with upturned flanges on the three almost straight sides, the fourth distal side bearing a pronounced lateral lobe on each side. Plate-scales (2-4 µm) fat ovals with a hint of radial furrowing and a central axial ridge.
Type locality: River Thames sediment, Oxford, UK.