Abundant, diversified algal assemblages comprising more than 25 species of Dasycladales are described from Barremian-Aptian limestone deposits of the Tirgan Formation in NE Iran. New species are described: one of them possibly belongs to a new endosporate genus, tentatively assigned the Triploporellaceae; two others, Clypeina ? sp. 1 and Rajkaella ? sp. 1, are left in open nomenclature. The widely distributed, locally abundant Montiella ? elitzae is revisited, because of the presence of a complete, exceptionally well preserved specimen. Yet to be demonstrated, the species is a junior synonym of Turkmenaria adducta Maslov, also originally described from the Kopet Dagh. Other species found in the Arkan section have already been reported from remote locations, primarily in Europe, in areas corresponding to the Northern and/or Southern Tethyan domains. Some of them are known only from the Hauterivian and/or the Barremian, excluding the Aptian, thus dating the lower part of the Arkan section as Barremian, but not excluding the Late Hauterivian.