Our acquaintance with this species is practically limited to the casts of stems. A typical stem of _E. columnaris_ measures 3 to 6 cm. in diameter and has fairly long internodes. The largest stem in the British Museum collection has internodes about 14 cm. long and a diameter of about 5 cm. In some cases the stem casts show irregular lateral projections in the neighbourhood of a node, but there is no evidence that the aerial shoots of this species gave off verticils of branches. In habit _E. columnaris_ probably closely resembled such recent species as _Equisetum hiemale_ L., _E. trachyodon_ A. Br. and others. The stems often show a distinct swelling at the nodes; this may be due, at least in part, to the existence of transverse nodal diaphragms which enabled the dead shoots to resist contraction in the region of the nodes. The leaf-sheaths consist of numerous long and narrow segments often truncated distally, as in fig. 58, _B_, and as in the sheath of such a recent Horse-tail as _E. ramosissimum_ shown in fig. 58, _C_. In some specimens one occasionally finds indications of delicate acuminate teeth extending above the limits of a truncated sheath. Brongniart speaks of the existence of caducous acuminate teeth in his diagnosis of the species, and the example represented in fig. 58, _B_, demonstrates the existence of such deciduous appendages. There is a very close resemblance between the fossil sheath of fig. 58, _B_, with and without the teeth, and the leaf-sheath of the recent _Equisetum_ in fig. 58, _C_. In some specimens of _E. columnaris_ in which the cast is covered with a carbonaceous film, each segment in a leaf-sheath is seen to be slightly depressed in the median portion, which is often distinctly marked by numerous small dots, the edges of the segment being flat and smooth. The median region is that in which the stomata are found and on which deposits of silica occur. 6. _Equisetites Beani_ (Bunb.). Figs. 60–62. Bunbury[518] proposed the name _Calamites Beani_ for some fossil stems from the Lower Oolite beds of the Yorkshire coast, which Bean had previously referred to in unpublished notes as _C. giganteus_. The latter name was not adopted by Bunbury on account of the possible confusion between this species and the Palaeozoic species _Calamites gigas_ Brongn. The generic name _Calamites_ must be replaced by _Equisetites_ now that we are familiar with more perfect specimens which demonstrate the Equisetean characters of the plant. [Illustration: FIG. 60. _Equisetites Beani_ (Bunb.). ⅔ nat. size. [After Starkie Gardner (86) Pl. IX. fig. 2.]]