The resemblance of sporangia and sori, whether preserved as carbonised impressions or as petrified material, from Carboniferous rocks, to those of recent species of Gleicheniaceae is in many cases at least the result of misinterpretation of deceptive appearances. Williamson[846] drew attention to the Gleichenia-like structure of some sections of sporangia from the English Coal-Measures, but he did not realise the ease with which sections of Marattiaceous sporangia in different planes may be mistaken for those of annulate (leptosporangiate) sporangia. In the regular dichotomous habit of Carboniferous fronds described as species of _Diplothmema_ (Stur) and _Mariopteris_ (Zeiller)[847] we have a close correspondence with the leaves of _Gleichenia_, but the common occurrence of dichotomous branching among ferns is sufficient reason for regarding this feature as an untrustworthy criterion of relationship. It is, however, interesting to find that in addition to the existence of some Upper Carboniferous ferns with sori like those of recent Gleichenias, the type of stelar anatomy illustrated by _Gleichenia dicarpa_ (fig. 237, C, p. 310) and other species is characteristic of the primary structure of the stem of the Pteridosperm _Heterangium_. We find in Carboniferous types undoubted indications of anatomical and other features which in succeeding ages became the marks of Gleicheniaceae. Some Carboniferous fronds with short and small pinnules of the _Pecopteris_ type, bearing sori composed of a small number of sporangia, have been assigned by Grand’Eury and other authors to the Gleicheniaceae; the same form of sorus is met with also on fronds with Sphenopteroid segments. The former is illustrated by _Oligocarpia Gutbieri_[848] and the latter by _O. Brongniarti_ described by Stur and by Zeiller[849]. Zeiller has described the circular sori of _Oligocarpia_ (fig. 270, B) as consisting of three to ten pyriform sporangia borne at the ends of lateral veins and possessing a complete transverse annulus, but Stur[850] believes that the annulus-like appearance is due to the manner of preservation of exannulate sporangia. In this opinion Stur is supported by Solms-Laubach[851] and by Schenk[852]. Despite an agreement between _Oligocarpia_ and _Gleichenia_, as regards the form of the sori and the number of sporangia, it is not certain that the existence of a typical Gleicheniaceous annulus has been proved to occur in any Palaeozoic sporangia[853].