The generic name _Heterangium_ was first used by Corda[206] for a piece of stem from the Coal Measures of Radnitz, Bohemia, represented by part of the vascular axis of a stem consisting of strands of large reticulately pitted tracheids intermixed with parenchyma and exhibiting structural features differing apparently from those of any known type. Corda’s material has been re-examined by Kubart[207] who figures a section from it. _Heterangium_ is a genus closely allied to _Lyginopteris_ both in habit and in general anatomical characters. The stem is monostelic; the vascular cylinder prior to secondary thickening resembles the protostele of certain recent species of _Gleichenia_ and may be compared also with _Trichomanes scandens_[208]. It agrees with that of _Lyginopteris_ in the possession of primary mesarch bundles but differs in the substitution of a cauline axial mass of metaxylem for the pith of _Lyginopteris_. The secondary vascular tissue agrees closely with that of recent Cycads and _Lyginopteris_. A characteristic feature is the occurrence of numerous horizontal bands of sclerous cells in the cortex (fig. 412) of the stem and in the ground-tissue of the rachis and larger branches of the fronds. The stem was erect and rarely branched ‘giving off large foliar appendages at somewhat distant intervals and from its entire circumference’[209]. Our knowledge of the reproductive organs is less precise than in the case of _Lyginopteris_; but we are justified in asserting that _Heterangium_ is a Pteridosperm which in all probability bore fern-like microsporangia and seeds similar in general plan to _Lagenostoma_. The association of some seeds included in Williamson’s genus _Conostoma_ with _Heterangium Grievii_ in the Pettycur beds and their resemblance to _Lagenostoma_, the seed of _Lyginopteris_, suggested the possibility of actual connexion: further evidence in support of this view has recently been brought forward by Dr Benson[210] in the case of a species of _Conostoma_ which she transfers to a new genus _Sphaerostoma_. The two species _Heterangium Grievii_ and _H. tiliaeoides_ are described in illustration of the genus and reference is made to a few other types. _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. 111, Pl. +xiv.+ fig. 2.] 1822. _Filicites_ (_Sphenopteris_) _elegans_, Brongniart, Class. Vég. p. 233. 1828. _Sphenopteris elegans_, Brongniart, Hist. Vég. Foss. p. 172. 1836. _Cheilanthites elegans_, Goeppert, Foss. Farnkr. p. 233. 1877. _Diplothmema elegans_, Stur, Culm Flora, +ii.+ p. 130. i. _Stem_.