The generic name Tichothecium Flotow, widely used for lichenicolous fungi, is found to be typified by Verrucaria nigrescens Pers. and so must be placed as a synonym of the lichen genus Verrucaria Schrader nom. cons. A preliminary survey of the fungi formerly referred to Tichothecium shows that they fall into two groups on the basis of the structure of the asci. Those with 4- or 8-spored, bitunicate asci are placed in Endococcus Nyl. (syn. Discothecium Zopf), while ones with multispored asci discharging by a bursting of the apex are considered to belong to Muellerella Hepp ex Müll. Arg. A provisional key to the 12 species of Endococcus treated is provided and notes on their nomenclature included. The new combinations E. alectoriae (D. Hawksw.), E. propinquus (Körber), E. ramalinarius (Lindsay), E. vermicularius (Lindsay), E. zahlbrucknerellae (Henssen), Muellerella lichenicola (Sommerf. ex Fr.), M. pygmaea (Körber), and Polycoccum arnoldii (Hepp) are made