495 
Origin of the U lodendroid Scar . 
for a very long period, and not to have been shed as in an ordinary Lepido- 
dendron , a fact which may be held to justify the removal of the species 
from Lepidodendron proper. 
The type with contiguous circular scars was referred by Dr. Kidston 
to Sigillaria . Here again, no specimen showing well-preserved leaf-scars 
has ever been figured, although specimens showing the cushions perfectly 
preserved are not uncommon. As in the former case, this fact raises 
a strong suspicion that the leaves were never shed by the intervention of an 
abscission layer. The specimens I have seen, although not conclusive, 
suggest that the leaf was only attached to quite a small area at the top of 
the leaf-cushion, instead of to a very large part of it as in Sigillaria. 
On the whole it is perhaps best to keep the genus Ulodendron, and to 
include in it both types, that with long leaf-bases, and that with short, square 
cushions. At the same time it must be understood that the difference 
between these and Lepidodendron is very small, probably consisting solely 
in the longer retention of the leaves. 
This long retention of the leaves is probably due to the fact that, when 
the whole branch was shed, it was unnecessary to make special arrangements 
for shedding each individual leaf. 
The fact that the specimen o {Lepidodendron fuliginosmn type described 
by Professor Weiss as a biserial Halonia has been identified by Kidston 
as Sigillaria discophora , an identification with which I agree, shows that 
Ulodendron , in its structure, approaches much more nearly to the Lepido- 
dendron type than it does to any form of Sigillaria . 
General Discussion of Halonia. 
It is of interest to consider the halonial branch in the light of our 
knowledge of Ulodendron. 
As has been recognized for many years, the two forms resemble one 
another in being lepidodendroid stems which have borne series of lateral 
appendages. Much confusion between the two types exists in the litera- 
ture, but when well preserved they are readily distinguished. As Dr. Kidston 
pointed out many years ago in a classical paper, Ulodendron has invariably 
its scars in two opposite rows, whilst in Halonia they are typically in a series 
of spirals running round the stem. Another difference which seems to me 
quite typical is that Halonia is very often found branching, forming in fact 
the ultimate branches of the tree, whilst only one branching specimen of 
Ulodendron seems to be known, and the stems always seem to be the main 
trunks, a conclusion which is proved in the case of the two vertical specimens 
in the Manchester Museum. 
Dr. Kidston has shown that all satisfactory specimens of Halonia 
belong to the genus Lepidophloios. 
