Spores simple. Apothecia with pore-like opening 1. *Perforaria Müll.-Arg. Apothecia with a wider opening 2. Pertusaria DC. Spores 1-septate 3. Varicellaria Nyl. XLV. _LECANORACEAE_ Thallus mostly crustaceous, occasionally squamulose or very rarely minutely fruticulose. The squamulose thallus is corticate above, the under surface appressed and attached to the substratum by penetrating hyphae, often effigurate at the circumference. Algal cells Protococcaceae. Apothecia well distinguished by the thalline margin; spores colourless, simple or variously septate or muriform. _Lecanora_, _Ochrolechia_, _Lecania_, _Haematomma_ and _Phlyctis_ are cosmopolitan genera, some of them with a very large number of species; the other genera are more restricted in distribution and generally with few species. The genus _Candelariella_ is of uncertain position; the spores are 8 or many in the ascus and are simple or 1-septate, and not unfrequently become polarilocular as in Caloplacaceae, but there is no parietin present. Algae distributed through the thallus. Spores simple 1. *Harpidium Koerb. Algae restricted to a definite zone. Spores simple. Thallus grey, white or yellowish. Spores rather small 2. Lecanora Ach. Spores large 3. Ochrolechia Massal. Thallus bright yellow. Spores simple or 1-septate 4. Candelariella Müll.-Arg. Spores 1-septate (rarely pluri-septate). Paraphyses free. Thallus squamulose, effigurate 5. Placolecania Zahlbr. Thallus crustaceous. Apothecial disc brownish 6. Lecania Zahlbr. Apothecial disc flesh-coloured 7. Icmadophila Trevis. Paraphyses branched, intricate 8. *Calenia Müll.-Arg. Spores elongate, pluri-septate. Apothecia superficial 9. Haematomma Massal. Apothecia immersed. Paraphyses free 10. *Phlyctella Müll.-Arg. Paraphyses branched, intricate 11. *Phlyctidia Müll.-Arg. Spores muriform. Apothecia superficial 12. *Myxodictyon Massal. Apothecia immersed 13. Phlyctis Wallr. XLVI. PARMELIACEAE A very familiar family of foliose lichens. Genera and species are dorsiventral and stratose in structure, though some _Cetrariae_ are fruticose in habit. Algal cells are Protococcaceae; in _Physcidia_ they are _Palmellae_. In every case the upper surface of the thallus is corticate and generally of plectenchyma, the lower being somewhat similar, but in _Heterodea_ and _Physcidia_, monotypic Australasian genera, the upper cortex is of branching hyphae parallel with the surface, the lower surface being non-corticate.