The first use of this name was by Artis[1083], who gave it to a long flattened cast, _Megaphyton frondosum_, found in Carboniferous strata in Yorkshire, characterised by two vertical rows of large scars and by impressions of sinuous roots. Kidston records the genus from the Middle and Upper Coal-Measures of Britain. A good example of this type of cast is afforded by _M. McLayi_ Lesq.[1084] from the Coal-Measures of North America, which has been recognised in European Carboniferous rocks. The leaf-scars are rounded or oval, broader than high; the vascular impression has the form of a closed ring (5–8 × 3–6 cm.), more or less circular and with a tendency to a rectangular outline, characterised by a deep inverted =U=-shaped sinus in the middle of the lower surface and by a =W=-shaped impression of an internal strand (fig. 298, B)[1085]. iii. _Ptychopteris_. This generic name, instituted by Corda[1086], is applied to decorticated stems of _Psaronius_, the surface of which is that of the vascular region on which the form of the leaf-scars is more or less clearly defined. The scar-areas are limited by an impression of the sclerenchymatous sheath enclosing the leaf-meristele, and internal to this is the impression of the leaf-trace. In some specimens a layer of coaly material which represents the carbonised cortex and adventitious roots covers the _Ptychopteris_ cast. The _Ptychopteris_ cast represented in fig. 299 shows the decorticated surface of part of a long stem on which the leaf-scars are arranged as in _Megaphyton_. An example of _Ptychopteris_ is figured by Fontaine and White[1087] from Virginia as _Caulopteris gigantea_. [Illustration: FIG. 299. _Ptychopteris._ ⅙ nat. size. From the Middle Coal-Measures of Lancashire. (The Manchester Museum.)] [Illustration: FIG. 300. _Dicksonia antarctica_ (half of stem in transverse section): _st_, stele; _s_, sclerenchyma.] _Position of_ Psaronius.