72 PTERIDOSPERMEAE [CH. 



Heterangium Grievii Williamson. 

 (Stem.). 



1872. Dictyoxylon Grievii, Williamson, Brit. Ass. Rep. (Edinburgh Meeting), 



p. 112. 



1873. Heterangium Grievii, Williamson, Phil. Trans. R. Soc. Vol. 162, p. 404. 



(Leaf.) 

 [1720. Fumaria officinalis, Volkmann, Silesia subterranea, p. Ill, PL xiv. 



fig. 2.] 



1822. Filicites (Sphenopteris) elegans, Brongniart, Class. Veg. p. 233. 

 1828. Sphenopteris elegans, Brongniart, Hist. V6g. Foss. p. 172. 

 1836. Cheilanthites elegans, Goeppert, Foss. Farnkr. p. 233. 

 1877. Diplothmema elegans, Stur, Culm Flora, n. p. 130. 



i. Stem. 



At the Edinburgh meeting of the British Association William- 

 son 1 gave a brief account of some petrified stems from the Lower 

 Carboniferous strata of Burntisland on the Firth of Forth which 

 he included in the genus Dictyoxylon. One of these was named 

 D. Grievii after Mr Grieve the discoverer of the specimens. In 

 a later and more complete description Williamson adopted Corda's 

 generic name on the ground of the close resemblance of the Scotch 

 stem to the Bohemian fragment Heterangium paradoxum. In 

 1873 2 Williamson added new facts in regard to H. Grievii and 

 in 1890 3 he described a very closely allied type from the Lower 

 Coal Measures of Lancashire. Five years later his descriptions 

 were considerably extended and modified in the joint memoir 

 with Dr Scott 4 . 



The great difference in age between the English Upper Car- 

 boniferous stem and the Scotch specimens from the Lower 

 Carboniferous beds of Burntisland suggests a probable specific 

 difference. Dr Scott has recently adopted the name Heterangium 

 Lomaxi, proposed but not published by Williamson, for the English 

 type. Though in the following account the species Heterangium 

 Grievii is treated in the broader sense it should be recognised that 

 the geologically younger stem is worthy of specific recognition; 

 it is characterised, to quote Scott 5 , by 'the great distinctness of 

 the primary xylem strands, by their nearly exarch structure, 



1 Williamson (72 2 ). 2 Williamson (73) A. 3 Williamson (90). 



4 Williamson and Scott (95). 5 Scott (15). 



