60 DR. D. H. SCOTT ON THE HETERANGIUMS 
remarkable for its perfect preservation, especially as regards the phloem 
(Williamson, 1887; Williamson & Scott, 1895). 
These two species, H. Grievii of Lower and H. tiliwoides of Upper Car- 
boniferous age, were the only British species recognised by Williamson in 
his published works. 
In 1890, however, he described some specimens from Dulesgate (Lower 
Coal Measures) under the name H. Grievii, and thus made this species range 
from the Lower to the Upper Carboniferous (Williamson, 1890). Williamson 
at first thought that some, at least, of these Dulesgate specimens were a 
different species, and gave them in MS. the name 77. Lomazii, but in his 
published account all are included under the name H. Grievii. The difficulty 
of identifying plants of such different horizons does not seem te have troubled 
Williamson at all. In the joint paper by Williamson and the present writer 
the same nomenclature was unfortunately adopted, though some distinctions 
between the Dulesgate and Burntisland forms were pointed out (Williamson 
& Scott, 1895, pp. 750 & 753). At the same time a Dulesgate specimen, 
differing somewhat from the others, was given the provisional name of 
H. cylindricum, though its claims to specific distinction were regarded as 
doubtful (Z. e. p. 765). 
In my ‘Studies in Fossil Botany’ (1st ed. 1900) it was recognised that 
Williamson’s Dulesgate specimens of “ Heterangium Grievii” probably repre- 
sented a separate species (Z. c. p. 345) ; in a second edition (1909, p. 410) 
Williamson's MS. name, HM. Lomawii, was definitely adopted for them. No 
full or critical account of the Dulesgate Heterangiums has, however, yet 
been given, and it is one object of the present communication to supply this 
omission. 
The stimulus to undertake a revision of British Coal-Measure Heterangiums 
was in part due to the discovery, in 1912, by Mr. Lomax, of a fine specimen 
of Heterangium from the coal-balls of Shore, Littleborough. This plant 
presents some remarkable features, and has aided in the interpretation of 
other forms ; it will be taken first in the description. 
The important discoveries of Dr. Kubart (1908; 1911; 1914), who has 
investigated a number of forms of Heterangium and Lyginopteris* from 
Upper Silesia, also render a survey of the British Coal-Measure species 
desirable. A consideration of Dr. Kubart's results (as yet only published in 
a preliminary form) will be postponed to the end of the paper; at the 
same time the species of Permo-Carboniferous age, previously discovered 
by Renault, will be dealt with. 
Some interesting points of comparison with the Lower Carboniferous 
genus Rhetinangium, discovered by Dr. Gordon (1912), also arise. 
* Potonié’s name is adopted in preference to the familiar Lyginodendron, Gourlie, for 
reasons fully set forth in Seward's * Fossil Plants,’ vol. iii. pp. 96-38 (1917). 
