Abstract
Description of a new diatom species, Сyclotella horstii Genkal et Kulikovskiy sp. nov., from Ivankovskoe reservoir (Volga reservoirs, Russia) is given. It is similar to Cyclotella ocellata Pantocsek and C. kuetzingiana Thwaites but can be distinguished by the size of the depressions and absence of papilio on the valve face, the arrangement of marginal fultoportulae and the size of vegetative and initial valves.