Abstract
A new diatom species, Cyclotella jonesii, is described from Pliocene freshwater deposits in the Klamath River Basin at Chiloquin, Oregon. It is clearly separated from most Cyclotella species by the distinctive rhomboid/elliptical shape of the valve. C. jonesii differs from the similarly shaped C. rhomboideo-elliptica Skuja in the marginal location of the rimoportula.