The apothecia are superficial, and are soft, waxy and bright-coloured, with prominent margins which are however entirely hyphal: the affinity is therefore with Lecideaceae. In one genus, _Sagiolechia_, the fruit is carbonaceous and dark coloured. The spores of all the genera are colourless. Apothecia waxy, bright-coloured. Thallus with _Scytonema_ gonidia. Spores elongate, 3-septate 1. Petractis Fr. Thallus with _Trentepholia_ gonidia. Asci 6-8-spored. Spores simple 2. Jonaspis Th. Fr. Spores 1-septate 3. *Microphiale A. Zahlbr. Spores septate or muriform 4. Gyalecta Ach. Asci 12-many-spored. Spores 1-septate 5. *Ramonia Stizenb. Spores fusiform or acicular, many-septate 6. Pachyphiale Lönnr. Apothecia carbonaceous. Spores elongate, 2-3-septate 7. *Sagiolechia Massal. XXX. _COENOGONIACEAE_ There are only two genera in this small family, _Coenogonium_ with _Trentepohlia_ gonidia, and _Racodium_ with _Cladophora_. Both genera follow the algal form and are filamentous. In _Coenogonium_ the filaments are sometimes matted into a loose felted expansion. The genus is mainly tropical or subtropical and mostly rather light-coloured. There is only one British species, _C. ebeneum_[1050], a sterile form, in which the hyphae are very dark-brown; it often covers large areas of stone or rock with its sooty-like creeping filaments. _Racodium_ includes 2 (?) species. One of these, _R. rupestre_, is sterile and resembles _C. ebeneum_ in form and colour. The apothecia of _Coenogonium_ are waxy and light-coloured; they are borne laterally on the filaments; the spores are simple or 1-septate. Thallus with _Trentepohlia_ gonidia 1. Coenogonium Ehrenb. Thallus with _Cladophora_ gonidia 2. Racodium Fr. XXXI. _LECIDEACEAE_ One of the largest lichen families as regards both genera and species, and of world-wide distribution. The algal cells are Protococcaceae. The thallus is mostly crustaceous but it becomes squamulose in _Psora_, a section of _Lecidea_; and in _Sphaerophoropsis_, a Brazilian genus, there are small upright fronds or stalks with lateral apothecia. The prevailing colour of the thallus is some shade of grey, but it ranges from white or yellow to dark-brown or almost black. Cephalodia appear in some of the species. The apothecia have a proper margin only, no gonidia taking part in the fruit-formation. They may be soft and waxy (biatorine) or hard and carbonaceous (lecideine). The genera are mainly based on spore characters which are very varied. The arrangement of genera given below follows that of Zahlbruckner; in several instances, both as to the limitations of genera and to the nomenclature, it differs from that of British text-books, though the general principle of classification is the same.