The striking feature exhibited by these Permian plants is the structure of the protostele, which in _Thamnopteris_ and probably in _Zalesskya diploxylon_ consists of solid xylem surrounded by phloem: this may be regarded as the primitive form of the Osmundaceous stele. In _Osmunda regalis_ and in other recent species of the genus the xylem cylinder has the form of a lattice-work; in other words, the departure of each leaf-trace makes a gap in the xylem and the overlapping of the foliar-gaps results in the separation of the xylem into a number of distinct bundles. In _Zalesskya gracilis_ the continuity of the xylem is not broken by overlapping gaps; in this it agrees with _Lepidodendron_. In _Thamnopteris_ the centre of the stele was occupied by a peculiar form of xylem obviously ill-adapted for conduction, but probably serving for water-storage and comparable with the short and broad tracheae in _Megaloxylon_[780]. There is clearly a well-marked difference in stelar anatomy between these two Permian genera and _Todea_ and _Osmunda_: this difference appears less when viewed in the light of the facts revealed by a study of the Jurassic species _Osmundites Dunlopi_. [Illustration: FIG. 251. _Lonchopteris virginiensis._ (After Fontaine. ½ nat. size.)] As possible examples of Triassic Osmundaceae reference may be made to some species included in Stur’s genus _Speirocarpus_[781]. _S. virginiensis_ was originally described by Fontaine[782] from the Upper Triassic rocks of Virginia as _Lonchopteris virginiensis_ (fig. 251) and has recently been figured by Leuthardt[783] from the Keuper of Basel. The sporangia, which are scattered over the lower surface of the pinnules, are described as globose-elliptical and as having a rudimentary apical annulus; no figures have been published. In habit the frond agrees with _Todites Williamsoni_, but the lateral veins form an anastomosing system like that in the Palaeozoic genus _Lonchopteris_ (fig. 290, B). There would seem to be an _a priori_ probability of this species being a representative of the Osmundaceae and not, as Stur believed, of the Marattiaceae. Seeing that _Lonchopteris_ is a designation of a purely provisional kind, it would be convenient to institute a new generic name for Triassic species having the Lonchopteris venation, which there are good reasons for regarding as Osmundaceous ferns. Similarly _Speirocarpus tenuifolius_ (Emmons) (= _Acrostichites tenuifolius_ Font.), which resembles _Todites Williamsoni_ (see p. 339) not only in habit and in the distribution of the sporangia but also in the venation, is probably an Osmundaceous species. _Osmundites._ _Osmundites Dunlopi_, Kidston and Gwynne-Vaughan[784], fig. 252.