The colonies are hypophyllous, up to 10 mm. or more in diam. or widely confluent, black, densely velvety. External mycelium of dark brown hyphae creeping over the leaf and forming stomopodia over the stomata, from which the internal mycelium enters the leaf and penetrates most of the mesophyll as intercellular, hyaline, septate hyphae which do not form haustoria in the host cells. Mycelial setae numerous, erect, mostly simple and obtuse to somewhat attenuate at the apex, up to 440 x 8-10 µ, or some forked irregularly with branches up to 120 µ long. Perithecia scattered amongst the mycelial setae, black, depressed-globose, the upper half bearing numerous erect-spreading simple black obtuse setae, up to 250 µ long; perithecia up to 500 µ diam. and 250 µ high, opening by a rounded pore at the vertex; the wall consists of an outer layer of rounded-polygonal cells which are slightly prominent, hence the surface appears slightly verrucose, passing internally into a hyaline mass of soft parenchyma, at first filling the whole interior. Within this soft tissue the fairly numerous asci develop from the base, replacing the original ground tissue, the remains of which form the more or less evanescent septate "paraphyses". Asci widely clavate to ovate, rounded at the apex and when young thickened there to 10 µ, nodose-stipitate below, 8-spored, about 150 x 50 µ. Spores cylindric to slightly ellipsoid, obtuse at the ends, dark brown, 3-septate, slightly constricted,. 45-55 x 18-21 µ, the cells approximately equal in length and the middle ones not noticeably swollen; end cells with the subterminal and sub-basal narrow hyaline bands usual in this genus.

Plagulae hypophyllae, usque ad 10 mm. diam., vel late confluentes, atrae, dense velutinae. Mycelium ex hyphis atrobrunneis, irregulariter ramosis, exhyphopodiatis, repentibus compositum, supra stomata folii stomopodia efformans et mesophyllum penetrans. Setae myceliales numerosae, erectae, simplices vel irregulariter furcatae, ramulis usque ad 120 µ longis, apice obtusae vel leniter attenuatae, usque ad 440 µ alt. et 8-11 µ cr. Perithecia dispersa, atra, depresso-globosa, usque ad 500 µ diam. et 250 µ alt., sursum setulosa; setae numerosae, simplices, atrae, obtusae, usque ad 250 µ longae; paries perithecii extus verrucosus, parenchymaticus, cellulis rotundato-polygonalibus, leniter prominentibus, atrobrunneis, intus in massam hyalinam mollem transeuntibus. Asci sat numerosi, basales, ereeci, ovati vel late clavati, apice rotundati, nodoso-stipitati, circa 150 x 50 µ, 8-spori. Paraphyses hyalinae, septatae, 3-5 µ cr., evanescentes. Sporae 2-3-seriatae, cylindraceo-ellipsoideae, utrinque obtusae, 3-septatae, leves, 45-55 x 18-21 µ.

Hab. in foliis Metrosiderodis excelsae, Rangitoto Is., Auckland, New Zealand, Dingley, July 1950, in Herb. Division of Plant Diseases, Auckland, N.Z.

The thyriothecia are completely superficial, epiphyllous, thin, flat, dark brown, circular, up to 280 µ diam., the wide margin much paler and consisting of very pale yellowish-brown wavy-reticulate hyphae about 2-3 µ wide, indistinctly septate, in a single layer, agglutinate to form a pellicle which extends over the whole ascoma, becoming darker towards the centre. Here it covers a rather loose weft of tangled hyaline hyphae 2 µ thick, much branched, in which the asci are embedded singly, though rather closely, apparently each in its own "locule". The asci are globose, sessile, thin-walled, 15-18 µ diam., 8-spored. Spores conglobate to nearly parallel, clavulate, 1-septate, slightly constricted, becoming dark brown when fully mature, 10-12 x 4.5-5 µ, the upper cell wider than the lower and subglobose, the lower slightly attenuate to the rounded base.

Thyriothecia superficialia, epiphylla, levia, applanata, brunneo-atra, orbiculata, usque ad 280 µ diam., margine pallidiora pelliculosaque. Mycelium liberum nullum. Asci in textu laxo hypharum hyalinarum singulariter subdenseque immersi sub pellicula myceliale, globosi, tenuiter tunicatae, 15-18 µ diam., 8-spori, sessiles. Sporae conglobatae vel subparallelae, clavulatae, 1-septatae, leves, brunnescentes, 10-12 x 4.5-5 µ.

Formerly this would have been placed in Eremotheca, but this genus is now considered not to be sufficiently distinct from Microthyriella.

Hab. in foliis Knightiae excelsae, Kapiti Is., Wellington, New Zealand, leg. H. H. Allan, November 1936.