Hyalopyrenia japonica Harada (lichenized Ascomycotina) is described as new genus on the basis of a specimen from friable rock in forests in Chiba-ken, central Japan. It is characterized by a poorly developed crustose thallus, a Trentepohlia phycobiont, immersed perithecia with hyaline walls, simple paraphyses and periphyses, non-amyloid bitunicate asci with an ocular chamber, and transversely septate hyaline spores. Hyalopyrenia is monotypic, and its taxonomic position is uncertain.