This and the following two families are distinguished by the pseudostroma or compound fruit, a character rare among lichens, though the true stroma is frequent in Pyrenomycetes in such genera as _Dothidea_, _Valsa_, etc. The genera are crustaceous and corticolous and occur with few exceptions in tropical or subtropical regions, mostly in the Western Hemisphere. Several grow on officinal bark (_Cinchona_, etc.). Algal cells are _Trentepohlia_. As in many tropical lichens, the spores are large. The genera are based chiefly on spore characters, on septation, and on the form of the spore cells: Spore cells cylindrical or cuboid. Spores colourless, elongate, multi-septate 1. *Tomasiella Müll.-Arg. Spores colourless, muriform 2. *Laurera Rehb. Spores brown, muriform 3. *Bottaria Massal. Spore cells globose-lentiform. Spores colourless, elongate, multi-septate 4. *Trypethelium Spreng. Spores brown, elongate, multi-septate 5. Melanotheca Müll.-Arg. X. _ASTROTHELIACEAE_ The perithecia are either upright or inclined, and occur usually in radiate groups. They are free or united in a stroma, and the elongate ostioles open separately or coalesce in a common canal. The genera are all crustaceous, with _Trentepohlia_ gonidia. They are tropical or subtropical, mostly in the Western Hemisphere; but species of _Parmentaria_ and _Astrothelium_ have been recorded also from Australia. The spores are all many-celled and the form of their cells is a generic character: Spores elongate, multi-septate. Spore cells cylindrical 1. *Lithothelium Müll.-Arg. Spore cells globose-lentiform. Spores colourless 2. *Astrothelium Trev. Spores brown 3. *Pyrenastrum Eschw. Spores muriform. Spores colourless 4. *Heufleria Trev. Spores brown 5. *Parmentaria Fée. XI. _MYCOPORACEAE_ A small family with only two genera which are found in both Hemispheres; species of both occur in Great Britain. They are all corticolous. The perithecia are united into a partially chambered fruiting body surrounded by a common wall, but opening by separate ostioles. The thallus is thinly crustaceous, with _Palmella_ gonidia in _Mycoporum_, and _Trentepohlia_ in _Mycoporellum_. The spores are colourless or brown in both genera: Spores muriform 1. Mycoporum Flot. Spores elongate, multi-septate 2. Mycoporellum A. Zahlbr. XII. _PHYLLOPYRENIACEAE_