128 LOWER DEVONIAN PLANT REMAINS 
3. Incertae Sedis 
(a) Axes with H-shaped Branching 
Plate VI, Fig. 23. 
Several examples showing H-shaped branching have been found 
in the deposit near Yankee Jim Creek. The finest of these has 
been selected for illustration at a magnification of four diameters 
in Plate VI, Fig. 23. Its relatively main axis, about 1-5 mm. 
wide, shows two lateral branches which lie closely parallel to one 
another. The “upper” branch need not be considered further as 
only a short length of it is exposed. The **lower"' appears to have 
divided by two successive dichotomies into two descending axes 
and one that was directed obliquely upwards. The descending limb 
(to the right in the photograph) shows further bifurcation into 
two more slender axes. 
H-shaped branching was first observed in Zosterophyllum 
myretonianum where direct continuity with fertile axes clearly 
demonstrated it to be a feature of the rhizomatous regions of that 
plant. When similarly branched disconnected axes of between 1-5 
and 2-5 mm. wide were found along with spikes and sporangia of 
Z. australianum at Mount Pleasant they were tentatively accepted 
and reeorded as belonging to that species. The question of the 
future identification of disconnected branch systems of this type 
has been discussed by Croft and Lang (1942, p. 155). These 
authors remark that “evidence is, however, steadily accumulating 
that this type of branching was widespread among early plants." 
This being so, considerable caution should now be exercised before 
axes with H-shaped branching are accepted as evidence of the 
presence of Zosterophyllum in a deposit. Following the example 
set in this respect by Croft and Lang, the specimens from Yankee 
Jim Creek are recorded as Incertae Sedis rather than as vegetative 
branches of Zosterophyllum australianum. 
(b) Pinnately-branched Axis 
Plate VI, Fig. 24. 
A few specimens from Mount Pleasant were grouped together 
under the heading ‘‘pinnately-branched axes." They are small 
portions of a new Siluro-Devonian plant, the nature of which has 
still to be discovered. 
A single specimen of this rare type has been found near Yankee 
Jim Creek. The specimen, shown enlarged ten diameters in Fig. 
24, though not as clearly defined nor as much branched as those 
from Mount Pleasant, is essentially of the same type of con- 
struction. It is a small curved axis about 1 em. long and 0-75 mm. 
