A comparison of _Psaronius_ with the Marattiaceae and other recent ferns leads to the conclusion that, on the whole, the evidence is in favour of the view usually held, namely that this genus is more closely related to the Marattiaceae than to any other recent ferns. It is, however, important not to overlook the differences between _Psaronius_ and recent genera of Marattiaceae, or the resemblances between the extinct genus and the Cyatheaceae. In habit _Psaronius_ agrees closely with recent tree-ferns; in the vascular system and in the sequence of events connected with the production of leaf-traces, there are striking resemblances between _Psaronius_ and the Cyatheaceous fern _Saccoloma adiantoides_ (= _Dicksonia Plumieri_ Hook.) as described by Mettenius[1088]. The piece of stem of _Dicksonia antarctica_ represented in fig. 300 exhibits a fairly close agreement with species of _Psaronius_, e.g. _P. infarctus_ (fig. 296, A, B). Moreover, the peripheral steles, which Zeiller has shown are confined to the stem and play an important part in the production of the roots and in the anastomoses with leaf-traces, are not represented in any Marattiaceous fern; on the other hand, they are comparable with the accessory strands met with in stems of recent Cyatheaceous tree-ferns[1089] (cf. fig. 240). The complex system of concentric dictyosteles is a feature more closely matched in _Angiopteris_ (Marattiaceae) than in any Cyatheaceous genus, the chief difference being in the more band-like form of the steles in _Psaronius_, though in a stem of _Angiopteris_ figured by Mettenius we see a close approach to the extinct type. The position of the protoxylem has unfortunately not been clearly defined in _Psaronius_ stems, but in _P. Renaulti_ it is stated by Scott[1090] to be endarch, a position which some of the protoxylem strands occupy in _Angiopteris_[1091]. The occurrence of large sieve-tubes described by Scott in _P. Renaultii_ is another feature shared by recent Marattiaceae. In many of the continental species of _Psaronius_ the phloem has not been preserved, and our knowledge of this tissue is comparatively meagre. In the Marattiaceae the roots arise mainly from the inner portions of the stele, while in _Psaronius_ they are usually formed from the external vascular bands. The formation of secondary cortical tissue is a peculiarity of _Psaronius_; on the other hand, if Butterworth[1092] is correct in referring to that genus the roots with secondary xylem, which he describes as _P. Cromptonensis_, a comparison may be made with the occurrence of secondary tracheae in the stem steles of _Angiopteris_[1093]. The absence of mechanical tissue in the stem of _Angiopteris_ is in contrast with its occurrence in the fossil stems and in recent tree-ferns; but this is a character of secondary importance and one which can be readily explained by the difference in habit between _Angiopteris_ and _Psaronius_.