Among the best known plants in the Palaeozoic floras are the genera _Lepidodendron_ and _Sigillaria_, types which are often spoken of as Giant Club-Mosses or as ancestors of existing species of _Lycopodium_ and _Selaginella_. Of these genera, but more particularly of _Lepidodendron_, we possess abundant records in a condition which have made it possible to obtain fairly complete information not only in regard to habit and external features but as to the anatomical characters of both vegetative and reproductive shoots. The structure of _Lepidodendron_ differs too widely from that of recent Club-Mosses (species of _Lycopodium_) to justify the statement that this prominent member of the Palaeozoic vegetation may be regarded as a direct ancestor of any living plant. There is at least no doubt that _Lepidodendron_ and _Sigillaria_ must be included in the Pteridophyta. The description by Dr Scott[236] of the genus _Lepidocarpon_, founded on petrified specimens of strobili, demonstrated the existence of a type of lycopodiaceous plant in the Carboniferous period distinguished from all living representatives of the group by the possession of integumented megaspores, which may fairly be styled seeds. _Lepidocarpon_ and another seed-bearing plant _Miadesmia_ are described under a separate heading as lycopodiaceous types characterised by an important morphological feature, which among recent plants constitutes a differentiating character between the Pteridophytes and the Phanerogams. Lepidodendron. i. _General._