Type:— USA. Idaho: Owyhee County, Chalk Hills Formation, USGS Diatom Locality 5244, (Circled specimen (Fig. 61) on CAS Slide #381069, material CAS Accession Number 602190 (CAS!), holotype, designated here).

Description: —Valves are circular, nearly flat, 10–23 µm in diameter, with a well-defined border between the central area and the marginal alveolate zone. Central area with a variable number of irregularly arranged areolae. Marginal zone extending from 1/3 to 1/2 of the valve radius consists of alveolate striae fascicles, 8– 12(14) in 10 µm, separated by hyaline interfascicles or costae. Striae fascicles are of equal length. They contain 3–4 rows of puncta, 40–60 in 10 µm. Alveoli are simple. Length of alveolar openings is not equal to the length of striae fascicles. Marginal fultoportulae with 3 satellite pores are located on every second–fourth costa separating alveolar openings internally. A single rimoportula occurs at one of the costae. Spines are present at the junction of the valve face and mantle at every interfascicle or costa.

Remarks: — Cyclotella pseudokansasica is similar to C. kansasica in the structure of alveolae, in the location of rimoportula and marginal fultoportulae, but differs by the absence of one more or less welldeveloped depression at the center, as well as by the shorter length of alveolar openings as compared with the length of striae fascicles.