Eight lichenicolous species of Arthonia from Tasmania are treated. Two are described as new: A. aurantia Kantvilas & Motiej., which infects the thallus of a Leprocaulon-like lichen and is characterised by vivid orange, K+ magenta ascomata, 0.07−0.1(−0.15) mm wide, and 1-septate, macrocephalic ascospores, 10−12.5(−13.5) × 4−5.5 μm; and A. endocarpa Kantvilas & Motiej., which infects the apothecia of Amandinea neoconglomerata Elix, and has non-amyloid asci interspersed with those of the host, and is characterised by 1-septate, macrocephalic ascospores, 8.5−13 × 4.5−6 μm. Two other species, A. epiphys­cia Nyl. and A. stictaria Nyl., are here recorded for Tasmania for the first time. Salient features of all species are compared.