Landsburgii_[99], from Carboniferous rocks at Stevenston in Ayrshire, Scotland, is represented in fig. 401. The convex areas represent casts of depressions in a reticulum of cortical tissue, originally occupied by comparatively delicate cells, which decayed or shrunk more quickly than the enclosing framework of stronger fibrous elements that remained as a prominent reticulum and produced the depressions bounding the raised portions of the cast. Such a cast would undoubtedly be formed by the stem on which Binney founded his species: the radially disposed bands of thick-walled cells seen in the outer part of the section (fig. 402) are portions of an irregular anastomosing mechanical system, the reticulate arrangement of which is seen in the impression of a rachis of a _Lyginopteris_ frond shown in fig. 405, E, and indicated in the more slender axis reproduced in fig. 404, A, _b_. This reticulate form of cortical stereome on which Brongniart founded the genus _Dictyoxylon_[100], a term since applied by Solms-Laubach and other authors to a certain type of cortex not confined to a single genus of plants, occurs also in some Palaeozoic lycopodiaceous stems[101] and in itself cannot be regarded as a safe criterion of botanical affinity. The largest example of Gourlie’s _Lyginodendron_ that has come under my notice is an incomplete sandstone cast from Upper Carboniferous strata near Harrogate reaching a length of 100 cm. and with convex areas 13 cm. long. A similar cast, 36 cm. broad, has recently been figured by Nathorst[102] from the Culm of Spitzbergen, and from the Upper Devonian of Ellesmere Land the same author has described impressions of a cortical reticulum under the name _Lyginodendron Sverdrupi_[103]. These specimens are interesting as pointing to the former occurrence in the Arctic regions of stems—probably Lepidodendroid—reaching the dimensions of a fairly large tree. As Potonié[104] pointed out, Gourlie’s generic name serves a useful purpose for casts of stems of the type shown in fig. 401 that cannot be assigned to a definite systematic position. The genus was first used for a specimen which has nothing to do with the plant usually spoken of as _Lyginodendron oldhamium_ (Binney). Though loath to give up a name by which Binney’s type has long been known, in spite of its retention in the second volume of this work I feel compelled so far to conform to the recognised principles governing nomenclature as to adopt Potonié’s generic term _Lyginopteris_. [Illustration: Fig. 401. _Lyginodendron Landsburgii_. (Kidston Coll. ¾ nat. size.)] _Lyginopteris oldhamia_ (Binney). i. _Stem_. 1866. _Dadoxylon oldhamium_, Binney, Proc. Lit. Phil. Manchester, vol. +v.+ p. 113. 1869. _Dictyoxylon oldhamium_, Williamson, Monthly Micros. Journ. vol. +ii.+ p. 66. 1873. _Lyginodendron oldhamium_, Williamson, Phil. Trans. Roy. Soc. vol. +clxiii.+ p. 404.