The designation _Parapitys_[778] has been proposed for a single Upper Carboniferous species characterised by the possession of secondary wood like that of _Cordaites_, double leaf-traces, and small mesarch primary xylem-strands. Nothing is known of the leaves or reproductive organs. _Parapitys Spenceri_ (Scott). In 1880 Williamson[779] published a short account of a transverse section of a specimen found by Mr J. Spencer in Upper Carboniferous strata near Halifax in Yorkshire which afforded evidence of the occurrence of double leaf-traces. The following description is taken from Scott’s account[780] of the species, which he named _Dadoxylon Spenceri_. The parenchymatous pith, 5–6 mm. in diameter, is obtusely pentagonal, the prominent angles corresponding to the points of exit of paired leaf-traces like those of _Mesoxylon_, _Ginkgo_, and other genera. The secondary xylem consists of narrow tracheids with crowded multiseriate pits on the radial walls and narrow medullary rays one-cell broad and 1–8 cells deep. In contact with the inner margin of the secondary wood are a few small mesarch strands of primary xylem, the protoxylem and some parenchyma occupying a more or less central position. A leaf-trace about to enter the secondary xylem is represented by twin-bundles which retain their double nature as they traverse the stele, but at a lower level the two components fuse and appear as single bundles at the outer edge of the pith. The division of a leaf-trace into two before passing out, as in _Poroxylon_, constitutes a difference from _Lyginopteris_ in which the division occurs later. Zalessky’s generic name _Parapitys_ is an appropriate substitute for _Dadoxylon_ in view of the presence of separate primary xylem strands, a feature foreign to typical Dadoxylons which agree with recent Conifers and Cycads in the absence of vascular strands distinct from the endarch centrifugal wood. As Scott[781] says, _Parapitys_ ‘is best regarded as a near ally of _Mesoxylon_.’ =Mesopitys.= Zalessky. _Mesopitys Tchihatcheffi_ (Goeppert). The genus _Mesopitys_ was instituted by Zalessky for a Permian species founded by Goeppert[782] on a piece of decorticated stem from the Kousnetzk basin in Siberia and afterwards more fully described by Goeppert and Stenzel[783]. The structure of the secondary wood led Goeppert to adopt the name _Araucarites_ for which Kraus[784] substituted _Araucarioxylon_. A recent investigation of additional material by Zalessky brought to light the existence of groups of primary xylem abutting on the secondary xylem and projecting into the pith, characterised by the occurrence of spiral protoxylem elements on the inner edge. The recognition of this important feature justified Zalessky in the adoption of a new generic term. In general anatomical characters _Mesopitys_ agrees with _Eristophyton Beinertianum_ (Goepp.) but is distinguished by the more feebly developed primary-xylem groups and by their endarch structure.