Pterocystis veliformis (Dürrschmidt, 1987) Siemensma, 1991
Diagnosis: Periplast, 10—20 µm in diameter (measurement based on whole mount), with two types of scales; details of protoplast unknown. The spine scales are reminiscent of a sail. The shaft is reduced to a short hollow rib. The lateral wings are continued along the whole length of the shaft reaching the maximum breadth in the lower 3rd of the scale. From here towards the proximal end they are closely anchylosed with the basal wing and form a short patternless stalk, sometimes only present as a concave depression around the proximal shaft end. The lateral wings are ornamented with thin, delicate ribs, which run transverselly or obliquely from the shaft to the outer margin. Ribs are also present on the front part but here they run inwards from the outer margin.
Plate scales are small, 0.9—1.3 x 0.6—0.8 µm, ovoid or, more rarely, elliptical. They are patternless except for an axial thickening which is slightly shifted to the smaller pole of the plate scale, and a narrow peripheral rim. As indicated by SEM micrograph they are not even but with distinctly concave middle parts, elevated submarginal parts and slightly inflexed margins.
Distribution: Chile, Canada.