can scarcely be regarded as mere spores. They should perhaps constitute a separate class or order to which the name _Nematodendreæ_ may be given, and of which _Nematophyton_ will constitute one genus and _Aporoxylon_ of Unger another.[N] [M] "Palæontologie des Thuringer Waldes," 1856. [N] See report by the author on "Erian Flora of Canada," 1871 and 1882, for full description of these fossils. Another question arises as to the possible relation of these plants to other trees known by their external forms. The _Protostigma_ of Lesquereux has already been referred to, and Claypole has described a tree from the Clinton group of the United States, with large ovate leaf-bases, to which he has given the name _Glyptodendron_.[O] If the markings on these plants are really leaf-bases, they can scarcely have been connected with _Nematophyton_, because that tree shows no such surface-markings, though, as we have seen, it had bundles of tubes passing diagonally to the surface. These plants were more probably trees with an axis of barred vessels and thick, cellular bark, like the _Lepidodendron_ of later periods, to be noticed in the sequel. Dr. Hicks has also described from the same series of beds which afforded the fragments of Nematophyton certain carbonised dichotomous stems, which he has named _Berwynia_. It is just possible that these plants may have belonged to the Nematodendreæ. The thick and dense coaly matter which they show resembles the bark of these trees, the longitudinal striation in some of them may represent the fibrous structure, and the lateral projections which have been compared to leaves or leaf-bases may correspond with the superficial eminences of _Nematophyton_, and the spirally arranged punctures which it shows on its surface. In this case I should be disposed to regard the supposed stigmaria-like roots as really stems, and the supposed rootlets as short, spine-like rudimentary leaves. All such comparisons must, however, in the mean time be regarded as conjectural. We seem, however, to have here a type of tree very dissimilar to any even of the later Palæozoic age, which existed throughout the Silurian, and probably further back, which ceased to exist early in the Erian age, and before the appearance of the ordinary coniferous and lepidodendroid trees. May it not have been a survivor of an old arboreal flora extending back even to the Laurentian itself? [O] "American Journal of Science," 1878.