This species, originally assigned to the genus _Stigmaria_, has a more strongly developed primary vascular system and there is a more decided tendency towards the formation of a continuous zone of primary xylem on the inner edge of the secondary wood; but where the protoxylem tracheids occur the metaxylem elements form definite strands, like those of _C. Saturni_. It has been pointed out by Scott and Jeffrey that there is some evidence of the occurrence of tracheids in the parenchymatous pith of this species, an important feature distinguishing it from _C. Saturni_ and connecting it with _C. americana_. Information with regard to the behaviour of the leaf-traces is far from complete, but there are indications that each trace divides into two before emerging from the secondary xylem[494]. The leaf-traces in the cortex are concentric as in _C. Saturni_. _Calamopitys americana_ Scott and Jeffrey. This Lower Carboniferous species[495] from the Waverley shales of Kentucky is represented by portions of stems and leaf-bases and detached petioles. The secondary wood consists of tracheids, 30–60μ in diameter, with deep and broad rays; the small pits on the tracheids form 5–6 alternating series. Phloem and cambium are very imperfectly preserved. The outer cortex is of the same type as in other species. At the inner edge of the secondary xylem there is a ring of primary xylem strands of mesarch structure composed of rather larger tracheids, 80–120μ in diameter, separated from one another by narrow strips of parenchyma. So far the vascular tissue agrees with that of _C. annularis_. In the American species the axial region is not a parenchymatous pith but a protostele, consisting of parenchyma and a larger or smaller number of tracheal groups, the number being less in stems with a larger central region. The peripheral strands alone are concerned with the emission of leaf-traces, as in _Heterangium_. Each primary xylem strand divides into two as it leaves the perimedullary zone and passes through the secondary xylem as two bundles, each being accompanied by an arc of secondary tracheids which, in the cortical region, completely surrounds the primary elements. At a later stage the single protoxylem of each trace divides into two and before entering the leaf-base there is a further division. In some specimens leaf-bases of the _Kalymma_ type were found attached to the stem. The occurrence of tracheids in the axial region is a distinguishing feature and suggests a comparison with _Heterangium_, while _C. Saturni_ agrees more closely with _Lyginopteris_; the species _C. annularis_ would appear, from the recent observations of Scott and Jeffrey, to occupy an intermediate position.