The comparison made by Nathorst with _Isoetes_ is based on a resemblance between the spores of the two genera and on the evidence, which is not decisive, of the existence of sterile strands of tissue in the sporangia of _Lycostrobus_. This similarity is however hardly of sufficient importance to justify the inclusion of the Rhaetic strobilus in the Isoetaceae. In size and in the arrangement and form of the sporophylls the cone presents a much closer resemblance to _Lepidodendron_ than to _Isoetes_. It is probably advisable to regard this Rhaetic type simply as a lycopodiaceous genus which we are unable, without additional information, to assign to a particular position. The opinion expressed by Professor Fliche[234] that the plant described by Schimper and Mougeot as _Caulopteris tessellata_, a supposed tree-fern stem, from Triassic rocks of Lorraine, is more probably a large lycopodiaceous stem, either a _Lepidodendron_ or a new genus, is worthy of note in reference to Nathorst’s account of _Lycostrobus_. In habit the fossil strobilus may be compared with the Triassic genus _Pleuromeia_, but the position of the sporangia on the sporophylls constitutes a well-marked difference. The most important result of Nathorst’s skillful treatment of this interesting fossil by chemical microscopic methods is the demonstration of the existence of a large heterosporous type of lycopodiaceous cone in a Rhaetic flora. Poecilitostachys. Under this generic name M. Fliche[235] has briefly described a fertile lycopodiaceous shoot from the Triassic rocks of Epinal in France: the type species _Poecilitostachys Hangi_ consists of a cylindrical axis, 10 cm. × 5 mm., deprived of leaves and terminating in a rounded receptacle bearing a capitulum of bracts or fertile leaves. Detached megasporangia containing small globular bodies found in association with the capitulum are compared with the megasporangia of _Isoetes_. CHAPTER XV. Arborescent Lycopodiales.