THE HETERANGIUMS OF THE BRITISH COAL MEASURES. 59 
The Heterangiums of the British Coal Measures. 
By D. H. Scorr, M.A., LL.D., F.R.S., FES! 
(PLATES 1-4.) 
[Read 19th April, 1917.] 
llzrERANGIUM is a genus of Carboniferous plants based on petrified speci- 
mens with the anatomical structure preserved ; it is now classed among the 
Pteridosperms. The characters of the genus are briefly as follows :— 
Stem monostelie; vascular cylinder a protostele, the primary xylem, inter- 
spersed with conjunctive parenchyma, extending to the centre and consisting 
throughout of elongated tracheides ; peripheral strands of stele and leaf-trace 
bundles mesarch, 
Secondary wood and bast formed. Tracheides (apart from the protoxylem- 
region) with multiseriate bordered pits. 
Leaf-trace bundles one or more for each leaf, 
Outer cortex consisting of alternating radial bands of sclerenchyma and 
parenchyma. 
Inner cortex, or pericycle, or both, usually with plates of sclereides. 
Leaves (when known) large, compound, and of the Sphenopteris type. 
This definition, while correct so far as it goes, will be found to need some 
emendation when the results of the present investigation are taken into 
consideration (see p. 99). 
The genus Heterangium was founded by Corda in 1845, on some fragments 
from the ** sphzero-siderites ” (coal-balls) of Radnitz in Bohemia, probably of 
Middle Coal-Measure age (Corda, 1845). Corda’s specimens showed little 
more than portions of the wood ; somewhat better examples of the species, 
H. paradoxum, have recently been obtained by Kubart from the same 
material (Kubart, 1911). 
In 1873 Williamson described in detail a fossil plant from the Pettycur 
deposits, near Burntisland, of Lower Carboniferous age; he referred his 
specimens to Corda’s genus, under the name Heterangium Grievii (William- 
son, 1873). This has now come to be the best-known species of the genus, as 
it is also the most ancient *. Williamson’s reference of his plant to Corda's 
genus was criticised by Renault (1879, p. 277), but has been confirmed by 
subsequent writers (Solms-Laubach, 1887; Kubart, 1911), and H. Grievii is 
now for practical purposes the type-species of Heterangiwum, though tech- 
nically 77. paradoxum, Corda, claims this position. 
Mucb later, in 1887, Williamson deseribed a species of Heterangium from 
the Halifax Beds (Lower Coal Measures). This was H. tiliwoides, a form 
* See also Williamson & Scott, 1895. 
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