The type-specimen consists of secondary xylem agreeing closely in structure with _Lyginopteris_ and recent Cycads: the pith, 2·9 cm. in breadth, is incompletely preserved; there is a narrow band of centripetal xylem[481] at the periphery of the perimedullary region and close to the inner face of the main mass of wood (fig. 453, C; the black line marks the position of the centripetal xylem). Nests of sclerous tissue and secretory canals are scattered in the medullary parenchyma and deeper in this region are arcs of secondary parenchyma, possibly periderm. In places the centripetal and centrifugal xylem are in contact and occasionally the tapered ends of the rows of centrifugal tracheids merge into groups of primary xylem elements. The preservation in the central region is far from complete, and although the occurrence of primary xylem groups is probable it cannot be said to be positively established. At the inner edge of the centrifugal xylem and in tangential longitudinal sections a few leaf-traces are seen, but nothing is known as to the nature of the leaf-traces in their course beyond the stele nor have we any data with regard to the leaves or reproductive organs. This older species differs from _Cycadoxylon Fremyi_ in the limitation of the centripetal xylem to the outer portion of the pith and in the presence of sclerous nests in the medullary region, though the latter character is probably of no great taxonomic value. _Cycadoxylon robustum_ approaches more closely to _Lyginopteris_, and although the differences are sufficient to justify a distinctive generic name, there can be little doubt as to a fairly intimate relationship between this type of _Cycadoxylon_ and _Lyginopteris_. =Ptychoxylon.= Renault.