Die Gattung Cosmarium 2: 127 (Krieger & Gerloff 1965).
DISTRIBUTION. — Brazil, Japan, Subantarctic Islands. Amazon Basin: Förster (1969); Thomasson (1977); Aprile & Mera (2007); Cadima (2013). Western Amazonia (lowlands): no records.
Cells 64.4-66.0 µm long, 42.0-42.8 µm wide, isthmus 15.0 µm; cells 1.5-1.6 times longer than wide. Cells with oval contour, deeply constricted in the median part, linear median sinus, narrow; pyramidal-subtruncate semicells, lateral margins slightly convex, apex broadly rounded, rounded basal and apical angles, hyaline, densely punctuated cell wall but not as finely as the type variety; axial chloroplast.
Our specimens coincided with the morphological characteristics and size presented by Krieger & Gerloff (1965) in their original description of the taxon. Also, they are similar in size to the populations described by Förster (1969) for the Brazilian Amazon, andOliveira de et al. (2010)for northeast Brazil.