Morphology of some fossil lacustrine centric species from the western United States assigned to the genus Cyclotella (Bacillariophyta), including four described as new Author Kociolek, J. P. University of Colorado Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, Colorado, 80309, USA Author Khursevich, G. K. Department of Botany, M. Tank Belarus State Pedagogical University, 18 Sovetskaya Street, 220809 Minsk, Republic of Belarus E? mail: galinakhurs. 41 @ mail. ru text Phytotaxa 2013 2013-08-29 127 1 81 99 http://dx.doi.org/10.11646/phytotaxa.127.1.11 journal article 10.11646/phytotaxa.127.1.11 1179-3163 5085519 Cyclotella pseudokansasica Khursevich & Kociolek , sp. nov. ( Figs 56–69 ) 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.