In 1894 Prof. Bertrand[671] published an account of certain fragments of petrified leaves and twigs of a small herbaceous Lycopodiaceous plant, under the name _Miadesmia membranacea_, which he discovered in English material in association with _Lepidodendron Harcourtii_. Subsequently Scott recognised the megasporophylls of the same plant, and microsporophylls have also been discovered. The most complete account of _Miadesmia_ so far published we owe to Dr Benson[672], whose description is based on specimens from several sources. _Miadesmia membranacea_, Bertrand. Fig. 219, A–D. [Illustration: FIG. 219. A–D _Miadesmia_; E _Bothrodendron_. A. Radial section of megasporophyll: _s_, sporangium; _m_, megaspore; _l_, ligule. (From a drawing kindly lent by Mrs D. H. Scott.) B, C. Leaf with ligule. (From a section in Dr Kidston’s Collection.) D. Transverse section of sporophyll. (After Scott.) E. Radial section of microsporophyll of _Bothrodendron_. (From a section in the Manchester Museum; Hick Collection R. 406.)] The slender stem, characterised by unequal dichotomy, has a single protostele composed of scalariform tracheids with 3–6 peripheral protoxylem groups. A zone of delicate tissue surrounds the xylem; this is described as phloem, but it is not clear whether the designation is based on histological characters or primarily on its position. The cortex consists of an inner lacunar tissue and an outer region limited by a small-celled superficial layer sharply contrasted with the underlying layers of larger cells. The stem of _Miadesmia_ is not uncommon in sections of the Lancashire calcareous nodules, and may be recognised by the delicate crushed tissue of which it mainly consists and by large hypodermal parenchyma. The spirally disposed leaves bear a conspicuous and relatively large ligule, 3 mm. long, in a deep pit (fig. 219, B and C) roofed over by a few layers of tissue corresponding to the velum in _Isoetes_ (cf. fig. 133, E, _v_). The fairly thick central region of the lamina is expanded laterally into thin wings, which in the living state probably bore delicate hairs. These delicate leaves, apparently without stomata, were attached to the stem at an acute angle, and Miss Benson suggests that their form and arrangement may have enabled them to hold water by surface-tension. As seen in fig. 219, B, C, which represents part of a transverse section near the leaf-base, the ligule is a very characteristic feature, and the size of the single vein is in keeping with the almost filmy nature of the lamina. In addition to the sections in British collections, I have been enabled by the kindness of Prof. Bertrand to see photomicrographs of the sections on which he founded the genus. One of these sections, transverse to the stem and leaves, illustrates in a striking manner the relatively large size of the leaves and ligules in proportion to the delicate axis of the shoot.