The large compound fronds long known as _Sphenopteris elegans_ were recognised by Kidston as the leaves of _Heterangium_ by the closely arranged transverse striae or narrow ribs on the rachis and pinnae which are the expression on the carbonised impressions of the horizontal plates of sclerous tissue in the petrified stems and petioles of _Heterangium_. The dichotomously branched fronds are included by Stur in his genus _Diplotmema_ and that author figures several typical examples in his ‘Culm Flora’[221]. Fig. 413, A, shows a forked axis with the bases of more slender branches and the characteristic transverse bands and in fig. 413, B, part of a pinna is reproduced. In general appearance, except in the bifurcating pinnae, the fronds resemble those of _Davallia tenuifolia_ with which Brongniart compared the Palaeozoic species. There is little doubt that _Sphenopteris dissecta_ and some other species were also borne on _Heterangium_ stems. The rachis and petioles differ from those of _Lyginopteris_ fronds in the absence of emergences (_cf._ fig. 404, E). The petioles (fig. 411, B, _a_) have a single concentric vascular bundle with internal protoxylem. [Illustration: Fig. 413. _Sphenopteris_ (_Diplotmema_) _elegans_. A. Forked rachis with bases of lateral branches (Kidston Coll.); B, pinna. (After Stur.)] iv. _Reproductive organs_. As yet no satisfactory evidence has been published with regard to the nature of the microsporangia but in all probability these were constructed on the same plan as those of _Lyginopteris_. There is a strong _prima facie_ case for assigning the seed _Sphaerostoma_ to _Heterangium_: absolute proof of organic connexion is still lacking though Dr Benson’s recent account of the seeds associated with _Heterangium Grievii_ almost amounts to demonstration of continuity between vegetative organs and seeds. _Sphaerostoma ovale_ (Williamson). [Illustration: Fig. 414. _Sphaerostoma ovale_. A. Longitudinal section showing the cupule, _c_, integument, _e_, _f_, with vascular bundle, _v_, the upper part of the nucellus, _n_, and megaspore, _m_; _a_, archegonia. B. Transverse section through the roof of the pollen-chamber, _pc_, and the summit of the nucellus, _n_. (After Benson.)]