Lang . — On the Morphology of Cyathodium . 413 
systematic arrangement of the forms of Cyathodium . A number of them 
differ from both C. cavernarmn and from C. aureo-nitens as defined by 
Griffith’s original diagnosis and specimens. My specimens from the caves 
at Kuala Lumpur agree, however, so closely with examples of C. cavernarum 
from Cuba that, with this explanation as to the locality in which they were 
collected, I shall refer to them below under this name. 
It is perhaps of greater morphological interest to make it clear at the 
outset that while C. foetidissimum is the largest and least reduced form in 
the genus, my specimens of C. cavernarum appear to be, if anything, even 
more reduced than those from Cuba. Thus a comparison can be made 
between one of the least reduced and the most reduced form in the genus. 
External Form and Vegetative Structure. 
The thallus of C. foetidissimum (Fig. 1) resembles in size and general 
appearance that of many Marchantiaceae, though its texture is more 
delicate. My specimens measured about 15 mm. in length by 4 mm. across. 
As a rule the plants had branched dichotomously, the two branches diverg- 
ing distinctly from one another. Seen from above, the surface is marked 
out into well-defined air-chambers. Those over the midrib are of regular 
outline and have the air-pore in a central position. On passing from the 
middle line the chambers become more irregular in shape, and the lateral 
ones are greatly extended over the marginal expansion of the thallus. In 
these lateral chambers the pore is near to the inner limit of the chamber, 
which is frequently divided by an imperfect septum running in from the 
edge of the thallus. Seen from below a narrow distinct midrib is visible, 
from which numerous rhizoids spring. The cells which are prolonged into 
rhizoids are conspicuous by reason of their dark brown colour. There are 
two rows of small ventral scales (cf. Fig. 9). The apical region lies in 
a depression owing to the greater development of the lateral portions of the 
thallus. The tips of the ventral scales bend up over the apex, but afford only 
an imperfect protection to it. 
In C. cavernarum (Fig. 25) the whole plant is much smaller ; my 
specimens were about 4 mm. in length. The thallus branches dichotomously, 
and the resulting branches may either be distinctly separated from one 
another, or repeated dichotomy with little separation of the branches may 
give a fan-shaped outline to the plant. The air-chambers are more irregular 
than in C. foetidissimum. There is no distinct midrib, its position being 
only indistinctly indicated by the attachment of the rhizoids and the 
inconspicuous ventral scales. 
Adventitious branches occur in both species (Figs. 2, 3). They 
originate from the under surface just within the margin of the thallus. Their 
base is cylindrical and some six cells in thickness, but they soon acquire 
the ordinary dorsiventral structure. 
