Only two genera are included in this family: _Nylanderiella_ with one species from New Zealand, with a small laciniate thallus up to 15 mm. in height, partly upright, partly decumbent, and attached to the substratum by basal rhizinae; the other small genus, _Pyrenothamnia_, belongs to N. America; the thallus has a short rounded stalk which expands above to an irregular frond. The perithecia are immersed in the fronds. Spores colourless, 1-septate 1. *Nylanderiella Hue[1039]. Spores brown, muriform 2. *Pyrenothamnia Tuckerm. VI. _MASTOIDEACEAE_ A family containing one genus and one species, with a wide distribution, having been found in Siberia, on the Antarctic continent (Graham’s Land), as also in Tierra del Fuego, South Georgia, South Shetland Islands and Kerguelen. The thallus is foliose, of small thin lobes, and without rhizinae. Algal cells _Prasiola_[1040]. The perithecia are globose and partly project from the thallus; the asci are 8-spored; the paraphyses are mucilaginous and partly dissolving. Spores elongate-fusiform, simple, colourless 1. *Mastoidea Hook. and Harv. VII. _PYRENULACEAE_ This family of crustaceous lichens differs from Verrucariaceae chiefly in the gonidium which is a species of _Trentepohlia_. Genera and species are largely corticolous and the thallus is inconspicuous, often developing within the substratum. The perithecia, like those of _Verrucariae_, are immersed or partly emergent and have an entire or dimidiate outer wall. They are scattered over the thallus except in _Anthracothecium_ where they are often coalescent. This genus is tropical or subtropical except for one species which inhabits S.W. Ireland. Paraphyses are variable, and in some species tend to disappear, but do not dissolve in mucilage. The spores are generally colourless, only in one monotypic genus, _Coccotrema_, are they simple. The cells into which the spore is divided differ in form according to the genus.