At the Edinburgh meeting of the British Association Williamson[211] 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[212] Williamson added new facts in regard to _H. Grievii_ and in 1890[213] 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[214]. The great difference in age between the English Upper Carboniferous 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[215], by ‘the great distinctness of the primary xylem strands, by their nearly exarch structure, with little primary centrifugal wood, by the abundant secretory sacs of the stele, and by the rather scattered leaves.’ [Illustration: Fig. 411. _Heterangium Grievii_. _lt_, _a_, _b_, _c_, leaf-traces; _p_, pericycle with periderm; _ph_, phloem; _x_¹, _x_², primary and secondary xylem; _px_, protoxylem; _r_, root; _s_, sclerous tissue.]