LOWER DEVONIAN PLANT REMAINS 127 
across so that the characteristic differentiation into medullary and 
cortical regions is revealed. The example is a slightly compressed 
spherical body, 6-5 mm. in diameter, the medulla being about 4 
mm. in diameter and the cortex about 2 mm. broad. The fine 
radial striations which were clearly visible in the better preserved 
specimen from Mount Pleasant cannot be distinguished in this 
example, but the way in which the carbonaceous material has split 
and broken away is quite consistent with a radial construction. 
Pachytheca is a rare fossil in the Southern Hemisphere. It has 
been found only in small numbers in the Mount Pleasant and Cen- 
tennial beds; its occurrence at a third, widely separated locality 
is therefore of interest. 
2. Zosterophyllum australianum 
Plate VI, Fig. 21. 
2. australianum is represented in this deposit by fertile spikes 
and detached sporangia. 
The unusually large and almost complete spike shown of natural 
size in Plate VI, Fig. 21, was found by a member of Dr. Harris’s 
party and presented to the Geological Museum, Melbourne. I am 
indebted to the Chief Geologist of the Mines Department, Dr. 
D. E. Thomas, for permission to examine and figure this very fine 
specimen. It consists of a smooth axis, 9 mm. broad and 2 em. long, 
and a terminal spike of a uniform width of 8 mm. and a length 
of 4.5 em. The tip of the spike is broken off. The sporangia are 
very numerous in the spike, some 35 being counted on the exposed 
surface. They are arranged in a close spiral and appear to be the 
same size throughout the spike. Those viewed abaxially show the 
typical reniform shape and the tangentially extended line of 
dehiscence. 
In general characters the specimen agrees with the type material 
from the Centennial beds (Lang and Cookson 1930). It differs in 
the greater length of the spike and the more numerous sporangia 
in it. In spite of the fact that the distal portion is missing, the 
fertile region is at least 2 cm. longer than any specimen known 
from either Walhalla or Mount Pleasant. The sporangia them- 
selves, though small (about 4 mm. across the widest part), are 
well within the limit for the species. The present specimen is 
distinctive for the unusually large number of sporangia that are 
crowded on the axis of the spike. Although the fertile spikes 
of Zosterophyllum australianum exhibit considerable variations, 
both in size of spike and the proportions and number of the indi- 
vidual sporangia comprising them, many more specimens will be 
necessary for comparison before specific distinctions are made. 
