OF THE BRITISH COAL MEASURES. 95 
species are not yet available *. The Ostrau specimens, which are admirably 
preserved, are very interesting from their age, which is somewhat earlier 
than that of our Lower Coal Measures, corresponding, according to Dr. 
Kubart, to the upper part of our Millstone Grit. The great point which his 
investigation has brought out is the existence of transitional forms between 
the genera Heterangium and Lyginopteris, confirming the close affinity 
between them, as maintained by Williamson and the present writer. Here, 
however, our point of view is somewhat different ; we are interested rather 
in the comparison between Dr. Kubart’s species and the British Coal- 
Measure Heterangiums. 
Five species of Heterangium from Ostrau are described—all appear to be 
new. The simplest structure is shown by H. Sturii, where there is practi- 
cally no differentiation in the stele between metaxylem and primary bundles 
(Kubart, 1914, p. 3, Taf. 2. fig. 3) ; the latter only become delimited when 
they begin to pass out as leaf-traces. The protoxylem, however, is nearly 
exarch. In the figure, five large leaf-traces are shown leaving the stele : all 
are single and no sign of division is to be observed ; evidently then, each 
leaf received a single bundle, and H. Sturii is a typical representative of the 
subgenus Eu-heterangium. It will be noticed that in this case a tendency to 
exarchy co-exists with an undifferentiated stele, contrary to what we found 
in the British Coal-Measure species. 
H. alatum $ has more or less well-defined peripheral primary bundles; their 
structure is typically mesarch, with well-developed centrifugal xylem. The 
leaf-traces are numerous (I counted 10 in the transverse section) and one 
bundle passed out into each leaf. A number of small winged petioles 
surrounded the stem, and are sometimes found still in connection with it. 
The secondary wood, when formed, is described as a perfectly continuous ring. 
H. alatum is thus an obvious member of the Eu-heterangium subgenus—the 
numerous small petioles give it, however, a very different character from 
H. Grievit. 
H. polystichum is a somewhat similar species {, with fairly distinct 
peripheral xylem-strands, which, like the leaf-trace bundles, are “ centrally 
mesarch,” i. e. with the protoxylem deeply imbedded. A single bundle leaves 
the stele for each trace ; the traces are very numerous, 13 appearing in the 
transverse section. The trace, on entering the leaf-base, may possibly 
have divided into two. The species evidently falls under the subgenus 
Eu-heterangium as defined above. — It is distinguished from H. alatum chiefly 
by a difference in the petioles. 
* Through Dr. Kubart's kindness, I have had an opportunity of examining sections of 
several of his species. 
+ Kubart, 1914, p. 2, Taf. 2. figs. 1, 2. 
+ Kubart, 1911, p. 11, Taf. 1. fig. 4; 1914, p. 4. 
