This generic name was proposed by Cotta in his classic work _Die Dendrolithen_[1054]. The stems so named, formerly included by Sprengel[1055] in the genus _Endogenites_, had long been familiar as petrified fossils. Most of the specimens described by the earlier writers were obtained from Lower Permian rocks in the neighbourhood of Chemnitz, Saxony. The mottled appearance presented by their polished surfaces is said to have given rise to the appellation _Staarsteine_ (starling stones), a term expressing a resemblance, more or less remote, to a starling’s breast. It has been suggested that this word is a corruption of _Stern Steine_ or star stones[1056], a descriptive term suggested by the stellate arrangement of the vascular strands in transverse sections of the roots. Parkinson[1057], in his _Organic Remains of a former World_, speaks of these stems as starry stones. The history of our knowledge prior to 1854 is summarised by Stenzel. At first compared with corals or the stems of sea-lilies, _Psaronii_ were recognised by Sprengel, who first used a lens in the examination of the fossils, as fern stems most nearly allied to those of recent Cyatheaceae. By other authors, e.g. Schlotheim and Sternberg, they were referred to Palms, and by Brongniart considered to be the lower portions of Lycopodiaceous (_Lepidodendron_) stems. Corda and many subsequent authors selected the Marattiaceae as the most closely allied family among existing plants. _Psaronius_ is represented by specimens obtained from the Lower Permian of Saxony and Upper Carboniferous rocks in Central France, also from Bohemia, Brazil and North America. As yet a few fragments only have been found in the English Coal-Measures. The genus was recognised by Williamson[1058] who described the roots and a small piece of the vascular tissue of a stem which he called _P. Renaulti_, and this type has since been more fully described by Scott[1059]. The roots of another species have been described by Butterworth[1060] as _P. Cromptonensis_. It was pointed out in the account of _Lepidodendron_ that several generic names have been used for the same type of stem in different states of preservation; in _Psaronius_ accidents of fossilisation have been responsible for a similar confusion in nomenclature. The name _Psaronius_ is applied to petrified specimens which, as a rule, lack external features. Casts or impressions of Palaeozoic tree-fern stems provided with leaf-scars are described as species of _Caulopteris_, _Megaphyton_, and less commonly as _Ptychopteris_ (figs. 297–299). The first name is applied to stems exhibiting spirally disposed leaf-scars like those of recent tree-ferns; in _Megaphyton_ the scars are distichously arranged, in two rows, while _Ptychopteris_ is applied to decorticated stems. These terms are used for stems belonging to one generic type and possessing the structure of Psaronius stems.