1. Equisetites Hemingwayi Kidst. Fig. 57, A.
Mr Kidston[503] founded this species on a few specimens of cones found in the Middle Coal-Measures of Barnsley in Yorkshire. The best example of the cone described by Kidston has a length of 2·5 cm., and a breadth of 1·5 cm.; the surface is divided up into several hexagonal areas 4 mm. high and 5 mm. wide. Each of these plates shows a fairly prominent projecting point in its centre; this is regarded as the point of attachment of the sporangiophore axis which expanded distally into a hexagonal plate bearing sporangia. An examination of Mr Kidston’s specimens enabled me to recognise the close resemblance which he insists on between the fossils and such a recent Equisetaceous strobilus as that of Equisetum limosum Sm. Nothing is known of the structure of the fossils beyond the character of the superficial pattern of the impressions, and it is impossible to speak with absolute confidence as to their nature. The author of the species makes use of the generic name Equisetum; but in view of our ignorance of structural features it is better to adopt the more usual term Equisetites.
Since Kidston’s description was published I noticed a specimen in the British Museum collection which throws some further light on this doubtful fossil. Part of this specimen is shown in fig. 57, A. The stem is 21 cm. in length and about 5 mm. broad; it is divided into distinct nodes and internodes; the former being a little exaggerated in the drawing. The surface is marked by fine and irregular striations, and in one or two places there occur broken pieces of narrow linear leaves in the neighbourhood of a node. Portions of four cones occurring in contact with the stem, appear to be sessile on the nodes, but the preservation is not sufficiently good to enable one to speak with certainty as to the manner of attachment. Each cone consists of regular hexagonal depressions, which agree exactly with the surface characters of Kidston’s type-specimen. The manner of occurrence of the cones points to a lateral and not a terminal attachment. The stem does not show any traces of Equisetaceous leaf-sheaths at the nodes, and such fragments of leaves as occur appear to have the form of separate linear segments; they are not such as are met with on Equisetites. It agrees with some of the slender foliage-shoots of Calamitean plants often described under the generic name Asterophyllites. As regards the cones; they differ from the known Calamitean strobili in the absence of sterile bracts, and appear to consist entirely of distally expanded sporophylls as in Equisetum. The general impression afforded by the fossil is that we have not sufficient evidence for definitely associating this stem and cones with a true Equisetites. We may, however, adhere to this generic title until more satisfactory data are available.
2. Equisetites spatulatus Zeill. Fig. 58, A.
This species is chosen as an example of a French Equisetites of Permian age. It was recently founded by Zeiller[504] on some specimens of imperfect leaf-sheaths, and defined as follows:—
Sheaths spreading, erect, formed of numerous uninerved coherent leaves, convex on the dorsal surface, spatulate in form, 5–6 cm. in length and 2–3 mm. broad at the base, and 5–10 mm. broad at the apex, rounded at the distal end.
The specimen shown in fig. 58, A, represents part of a flattened sheath, the narrower crenulated end being the base of the sheath. The limits of the coherent segments and the position of the veins are clearly marked. Zeiller’s description accurately represents the character of the sheaths. They agree closely with an Equisetaceous leaf-sheath, but as I have already pointed out, we cannot feel certain that sheaths of this kind were not originally attached to a Calamite stem.
The portion of a leaf-sheath and a diaphragm represented in fig. 57, B, agrees closely with Zeiller’s examples. This specimen is from the English Coal-Measures, but it is not advisable to attempt any specific diagnosis on such fragmentary material. It is questionable, indeed, if these detached fossil leaf-sheaths should be designated by specific names. Another similar form of sheath, hardly distinguishable from Zeiller’s species, has recently been described by Potonié from the Permian (Rothliegende) of Thuringia.
Fig. 58.