Stem reaching a diameter of 2–3 cm. with internodes as much as 4 cm. long, the surface of which is traversed by longitudinal ridges and grooves which are continuous and not alternate at the nodes. Branches arise in verticils from the nodes. The leaves have the form of funnel-shaped sheaths split up into narrow and spreading linear segments, each of which is traversed by a median vein. The fertile shoot terminates in a loose strobilus bearing alternating whorls of sterile bracts and sporangiophores. The specimens on which this diagnosis is founded are for the most part fragments of sterile branches. Some of these present the appearance of Calamitean stems in which the ridges and grooves continue in straight lines from one internode to the next. Similar stem-casts have been referred by some writers to the allied genus _Schizoneura_, and it would appear to be a hopeless task to decide with certainty under which generic designation such specimens should be described. The portion of stem shown in fig. 67 affords an example of an Equisetaceous plant, probably in the form of a cast of a hollow pith, which might be referred to either _Phyllotheca_ or _Schizoneura_. The specimen was found in certain South African rocks which are probably of Permo-Carboniferous age[557]. It agrees closely with some stems from India described by Feistmantel[558] as _Schizoneura gondwanensis_, and it also resembles equally closely the Australian specimens referred by Feistmantel[559] to _Phyllotheca australis_ and some stems of _Phyllotheca indica_ figured by Bunbury[560]. The longitudinal ridges and grooves shown in fig. 67 probably represent the broad medullary rays and the projecting wedges of secondary wood surrounding a large hollow pith, as in _Calamites_. In the Calamitean casts the ridges and grooves of each internode usually alternate in position with those of the next, as in _Equisetum_ (fig. 54, A), but in _Phyllotheca_, _Schizoneura_ and _Archaeocalamites_ there is no such regular alternation at the nodes of the internodal vascular strands. [Illustration: FIG. 67. _Phyllotheca?_ ¾ nat. size. From a South African specimen of Permo-Carboniferous age in the British Museum.] In _Phyllotheca_ and _Schizoneura_ there are no casts of ‘infranodal canals’ below each nodal line, but these are by no means always found in true Calamites. It is therefore practically impossible to determine the generic position of such fossils as that shown in fig. 67 without further evidence than is afforded by leafless casts.