Only one genus is represented in the British Isles.
| Apothecia growing singly. | ||
| Thallus with Trentepohlia gonidia. | ||
| Paraphyses numerous, unbranched, free. | ||
| Spores colourless. | ||
| Spores elongate, 2- or multi-septate | 1. | *Ocellularia Spreng. |
| Spores muriform | 2. | Thelotrema Ach. |
| Spores brown. | ||
| Spores elongate, septate | 3. | *Phaeotrema Müll.-Arg. |
| Spores muriform | 4. | *Leptotrema Mont. |
| Paraphyses scanty, branched. | ||
| Spores muriform, brown | 5. | *Gyrostomum Fr. |
| Thallus with Phycopeltis gonidia | 6. | *Phyllophthalmaria A. Zahlbr. |
| Apothecia in pseudostromata. | ||
| Apothecia united in tubercles | 7. | *Tremotylium Nyl. |
| Apothecia united by the margins | 8. | *Polystroma Clem. |
XXVII. Diploschistaceae
Scarcely differing from the preceding family except in the gonidia which are Protococcaceous algae. The thallus is crustaceous and non-corticate. The apothecia have a double margin but the outer thalline margin is less overarching than in Thelotremaceae. The spores in the two genera are somewhat peculiar: in Conotrema they are exceedingly long and divided by parallel septa into thirty to forty small cells; in Diploschistes (Urceolaria) they are large, muriform and brown. Conotrema contains two corticolous species; Diploschistes about thirty species mostly saxicolous. Both genera are represented in the British Isles.
| Spores elongate, multi-septate, colourless | 1. | Conotrema Tuck. |
| Spores muriform, brown | 2. | Diploschistes Norm. |
XXVIII. Ectolechiaceae
A family of tropical epiphyllous lichens that are associated with Protococcaceous gonidia. The thallus is primitive in character, mostly a weft of hyphae with intermingled algal cells, described as homoiomerous.
The apothecia are without a thalline margin, and with a scarcely developed proper margin: their affinity is with the Lecideaceae, though in two genera, Lecaniella and Arthotheliopsis, there are gonidia below the hypothecium, a character of Lecanoraceae. The genera are nearly all monotypic; in Sporopodium has been included Lecidea phyllocharis Wainio (Sect. Gonothecium), which is distinguished by hymenial gonidia.
| Apothecia at first covered by a “veil.” | ||
| Spores elongate, colourless, septate | 1. | *Asterothyrium Müll.-Arg. |
| Apothecia uncovered from the first. | ||
| Gonidia not present below the hypothecium. | ||
| Paraphyses unbranched, free. | ||
| Spores muriform | 2. | *Lopadiopsis Wain. |
| Paraphyses branched. | ||
| Spores 1-septate | 3. | *Actinoplaca Müll.-Arg. |
| Spores elongate, multi-septate | 4. | *Tapellaria Müll.-Arg. |
| Spores muriform | 5. | *Sporopodium Mont. |
| Gonidia present below the hypothecium. | ||
| Spores elongate, 2-septate | 6. | *Lecaniella Wain. |
| Spores muriform | 7. | *Arthotheliopsis Wain. |