Descriptions are provided for two new species, Mycomicrothelia lateralis Sipman from Norfolk Island and M. triangularis Aptroot from Puerto Rico, both characterized by lateral ostioles and uniseriate ascospores. Based on the examination of additional fresh material, the genus Ornatopyrenis is included in Mycomicrothelia and the new combination Mycomicrothelia queenslandica (Müll. Arg.) Sipman & Aptroot is made. Ornatopyrenis muriformis Aptroot is proposed as a synonym of M. decipiens (Müll. Arg.) R. C. Harris.