Thallus with _Gloeocapsa_ gonidia. Thallus crustaceous. Spores simple 1. Pyrenopsis Nyl. Spores 1-septate 2. *Cryptothele Forss. Thallus shortly fruticose 3. Synalissa Fr. Thallus lobate, centrally attached 4. *Phylliscidium Forss. Thallus with _Chroococcus_ gonidia. Thallus crustaceous 5. Pyrenopsidium Forss. Thallus lobate, centrally attached 6. *Phylliscum Nyl. Thallus with _Xanthocapsa_ gonidia. Thallus crustaceous. Thallus non-corticate. Spores simple. Apothecia open, asci 8-spored 7. Psorotichia Forss. Apothecia covered, asci many-spored 8. *Gonohymenia Stein. Spores 1-septate. Apothecia closed 9. *Collemopsidium Nyl. Thallus with plectenchymatous cortex 10. *Forssellia A. Zahlbr. Thallus lobate, centrally attached. Spores simple. Thallus plectenchymatous throughout 11. *Anema Nyl. Thalline tissue of loose hyphae 12. *Thyrea Massal. Cortex of upright parallel hyphae 13. *Jenmania Wächt. Spores 1-septate. Thalline tissue of loose hyphae 14. *Paulia Fée. Thallus fruticose. Thallus without a cortex 15. *Peccania Forss. Thallus with cortex of parallel hyphae 16. *Phloeopeccania Stein. XXXVIII. _LICHINACEAE_ The only family of lichens associated with _Rivularia_ gonidia, the trichomes of which retain their filamentous form to some extent in the more highly developed genera; they lie parallel to the long axis of the squamule or of the frond except in _Lichinella_ in which genus they are vertical to the surface. The thallus may be crustaceous, or minutely foliose, or fruticose; in all cases it is dark-brown in colour, and the gelatinous character is evident in the moist condition. The best known British genus is _Lichina_ which grows on rocks by the sea. The apothecia are more or less immersed in the tissue; in _Pterygium_ and _Steinera_ they are open and superficial (the latter monotypic genus confined to Kerguelen). They are also open in _Lichinella_ and _Homopsella_, both very rare genera. The spores are colourless and simple except in _Pterygium_ and _Steinera_ where they are elongate, and 1-3-septate.