In a previous communication (NAIR, 1964) some of the common Nostocaceae of Kanpur have been described . While studying the phytoplankton of river Ganges in connection with their control, a number of planktonic Nostocaceae were observed and the present paper deals mainly with the systematics of these forms . In all 14 forms have been described belonging to Anabaena, Anabaenopsis, Aphanizomenon and Raphidiopsis.
Of the six species of Anabaena, Anabaena planctonica has been described for the first time from India . It forms one of the dominant algae in Ganges during summer . This alga has been reported to form waterblooms in other countries also (GRIFFITHS, 1925 ;GuPTA, 1955) . The presence of this planktonic form both in temperate and tropical countries shows that it has a wide distribution . Anabaena kwangtungensis, which is not uncommon in Northern Kwangtung, was not reported from India earlier .
Anabaenopsis is a common planktonic alga which is responsible for water blooms, and it occurs both in flowing and stagnant waters . Of the four species, Anabaenopsis arnoldii, the type species, has been recorded for the first time from India . A new variety of Anabaenopsis circularis was found to be common in both the Ganges and in the puddles formed by the receeding water . Anabaenopsis gangetica is a new species more abundant in the puddles than in the flowing water . The common Anabaenopsis raciborskii, however, occupies an isolated position . The heterocysts in this form never originate in an intercalary position characteristic of the genus but are formed out of the