The new genus Aglaothecium Groenh. is proposed to accomodate the new species A. saxicola Groenh. The development of bitunicate asci as occurring in cryptothecioid genera is compared with that of the supposedly unitunicate but thick-walled asci which are common in Lecideaceae and Lecanoraceae. The question is discussed whether bitunicate asci are always indifferent to iodine.