New specimens of Subterraniphyllum thomasii Elliott collected from the Oligocene Molare Formation outcropping close to Alessandria (northern Italy) and studied in thin sections and by SEM showed that primary pit-connections, cell fusions, uniporate conceptacles and geniculate branches were present. These new observations collectively confirm the placement of S. thomasii within the geniculate Corallinaceae. Although S. thomasii share many diagnostic characters with the Corallinoideae, in particular with the tribe Corallineae (apical position of uniporate conceptacles, number of medullary cell layers) and some similarity with the Metagoniolithoideae (medullary cells gradually merging into the cortical cells) the lack of information on genicula and the observed details of insertion of branches do not allow to determine the suprageneric disposition of S. thomasii. 
