68 Transactions British Mycological Society. 
is about 165, in diameter. They have a regularly radiate 
structure and the margin is entire, or very slightly crenate, but 
never fimbriate. None of the specimens show a definite ostiole, 
but this may be due to immaturity, while on the other hand 
there is an appearance in some ascostromata of an irregular 
dehiscence such as occurs in some recent members of the family, 
e.g. Asterina, but appearances in fossils such as this are liable 
to be deceptive, and might be due to post-mortem or post- 
fossilization changes. There is no mycelium on the surface of 
the leaf, but stigmocysts (Pl. VIII, figs. 5 and 6) are abundant, 
and all stages of growth are to be found between them and the 
largest of the ascostromata. The stigmocysts (unicellular capi- 
tate hyphopodia) are circular and deeply crenulate, about 
10-12 pw in diameter, and the clear central spot is usually dis- 
tinctly seen. 
No asci have so far been found, but Pl. VIII, fig. 7 shows a 
large 5-celled spore (? ascospore), 43 in length and 25, in 
breadth, which appears to be sending out delicate hyphae at 
each end. Another slide shows a similar spore, rather shrunken, 
with apparently only four cells. It seems quite probable that 
these spores belong to the same species as the ascostromata, 
though of course one cannot be absolutely certain. At any rate 
there is no other recognisable fungus on the leaves to which 
they might belong. There are a few detached fragments of 
hyphae and some spore-like bodies which may perhaps be men- 
tioned here, but which may not even be of fungal nature. 
The reference of a fossil fungus to its exact systematic position 
is not an easy matter, even when the material is so well pre- 
served. as in the present case. There are certain characters 
which are used in the classification of recent fungi which cannot 
be observed in a fossil, e.g. the colour of the spores, and more- 
over dissociated objects cannot always be proved absolutely to 
belong to the same species. In this instance one can at least 
feel fairly certain that the fossil is to be placed in the Micro- 
thyriaceae, though the exact generic reference is more difficult. 
The Microthyriaceae and other “‘asterinoid”’ fungi have re- 
ceived considerable attention of late years, and their classifi- 
cation and relationships have been critically studied and revised 
by von Hohnel, Theissen, Arnaud and others. Desmaziéres’ 
genus Microthyrium (1841) was made the type of the family 
Microthyriaceae by Saccardo in 1883, and this family subse- 
quently became the dumping ground for many heterogeneous 
forms which have since been excluded, while on the other hand 
detailed study has resulted in the separation of many new 
genera. The classification of Theissen (1913, 1 and 1913, 2) 
forms the basis of our present knowledge. He groups together 
