- Equisetites spatulatus, Zeill. Leaf-sheath. ⅘ nat. size. (After Zeiller.)
- E. columnaris, Brongn. From a specimen in the British Museum. ¾ nat. size.
- Equisetum ramosissimum, Desf. × 2.
- Annularia stellata (Schloth.). Leaf-sheath. Slightly enlarged. (After Potonié.)
- Equisetites zeaeformis (Schloth.). Leaf-sheath. ⅘ nat. size. (After Potonié.)
- E. lateralis, Phill. From a specimen in the Scarborough Museum. Nat. size.
3. Equisetites zeaeformis (Schloth.)[505] Fig. 58, E.
The sheaths consist of linear segments fused laterally as in Equisetum. In some specimens the component parts of the sheath are more or less separate from one another, and in this form they are apparently identical with the leaves of Calamites (Calamitina) varians, Sternb. The example shown in fig. 58, E is probably a young leaf-sheath; the segments are fused, and each is traversed by a single vein represented by a dark line in the figure. The regular crenulated lower margin is the base of the sheath, and corresponds to the upper portion of fig. 58, A. This species affords, therefore, an interesting illustration of the difficulty of separating Equisetites leaves from those of true Calamites. Potonié has suggested that the leaf-sheath of a young Calamite might well be split up into distinct linear segments as the result of the increase in girth of the stem.
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Other Palaeozoic species of Equisetites have been recorded, but with one exception these need not be dealt with, as they do not add anything to our knowledge of botanical importance. The specimen described in the Flore de Commentry as Equisetites Monyi, by Renault and Zeiller[506], differs from most of the other Palaeozoic species of Equisetites, in the fact that we have a stem with short internodes bearing a leaf-sheath at each node divided into comparatively long and distinct teeth. This species presents a close agreement with specimens of Calamitina, but Renault and Zeiller consider that it is generically distinct. They suggest that the English species, originally described and figured by Lindley and Hutton[507] as Hippurites gigantea, and now usually spoken of as Calamitina, should be named Equisetites. It would probably be better to adopt the name Calamitina for the French species. The type-specimen of this species is in the Natural History Museum, Paris.
EQUISETITES PLATYODON.
Fig. 59. Equisetites platyodon Brongn. (After Schoenlein, slightly reduced.)
When we pass from the Permian to the Triassic period, we find large casts of very modern-looking Equisetaceous stems which must clearly be referred to the genus Equisetites. The portion of a stem represented in fig. 59 known as Equisetites platyodon Brongn.[508] affords an example of a Triassic Equisetaceous stem with a clearly preserved leaf-sheath. The stem measures about 6 cm. in diameter. One of the oldest known Triassic species is Equisetites Mougeoti[509] (Brongn.) from the Bunter series of the Vosges.
The Keuper species E. arenaceus is, however, more completely known. The specimens referred to this species are very striking fossils; they agree in all external characters with recent Horse-tails but greatly exceed them in dimensions.