Abstract
Reimeria sinuata (Greg.) Kociolek & Stoermer is split into two species. The valve structure of materials from Argentina was studied in the SEM and compared with others from South Africa, North America and Europe and also with other taxa of the genus Reimeria. The specific characteristics of Reimeria uniseriata nov. spec, are uniseriate striae; 16-30 areolae in 10 μm with C-shaped foramina and one apical pore field in each pole, positioned over the mantle and valve face.