The fossils included under Archaeocalamites have been referred by different authors to various genera, and considerable confusion has arisen in both generic and specific nomenclature. The following synonomy of the best known species, A. scrobiculatus (Schloth.) illustrates the unfortunate use of several terms for the same plant.

1720.Lithoxylon, Volkmann[842].
1820.Calamites scrobiculatus, Schlotheim[843].
1825.Bornia scrobiculata, Sternberg[844].
1828.Calamites radiatus, Brongniart[845].
1841.Pothocites Grantoni, Paterson[846].
1852.Calamites transitionis, Göppert[847].
——Stigmatocanna Volkmanniana, ibid.
——Anarthrocanna tuberculata, ibid.
——Calamites variolatus, ibid.
——C. obliquus, ibid.
——C. tenuissimus, ibid.
——Asterophyllites elegans, ibid.
1866.Calamites laticulatus, Ettingshausen[848].
——Equisetites Göpperti, ibid.
——Sphenophyllum furcatum, ibid.
1873.Asterophyllites spaniophyllus, Feistmantel[849].
1880.Asterocalamites scrobiculatus, Zeiller[850].

For other lists of synonyms reference may be made to Binney[851], Stur[852], Kidston[853] and other authors.

Some of the best specimens of this species are to be seen in the Museums of Breslau and Vienna, which contain the original examples described by Göppert and Stur. An examination of the original specimens, figured by Göppert under various names, enables one to refer them with confidence to the single species, Archaeocalamites scrobiculatus. The generic name Archaeocalamites, which has been employed by some authors, was suggested by Schimper[854] in 1862, as a subgenus of Calamites, on account of the occurrence of a deeply divided leaf-sheath, attached to the node of a pith-cast, which seemed to differ from the usual type of Calamitean leaf. The specimens described by Schimper are in the Strassburg Museum; the leaf-sheath which he figures is not very accurately represented.

The example given in fig. 103 shews very clearly the continuous course of the ribs and grooves of the pith-cast. Each rib is traversed by a narrow median groove which would seem to represent the projecting edge of some hard tissue in the middle of each principal medullary ray of the stem. The specimen was found in a Carboniferous limestone quarry, Northumberland; there is a similar cast from the same locality in the Museum of the Geological Survey.

Affinities of Archaeocalamites.

This genus agrees very closely with Calamites both in the anatomical structure of the stem and in the verticillate disposition of the leaves. The strobili appear to be Equisetaceous in character, and there is no satisfactory evidence of the existence of whorls of sterile bracts in the cone, such as occur in Calamostachys and in other Calamitean strobili. The continuous course of the vascular bundles of the stem from one internode to the next is the most striking feature in the ordinary specimens of the genus; but it sometimes happens that the grooves on a pith-cast shew the same alternation at the node as in Calamites. This is the case in a specimen in the Göppert collection in the Breslau Museum, and Feistmantel[855] has called attention to such an alternation in specimens from Rothwaltersdorf. In the true Calamites, on the other hand, the usual nodal alternation of the vascular strands is by no means a constant character[856]. Stur[857], Rothpletz[858], and other authors have pointed out the resemblance of Archaeocalamites to Sphenophyllum. The deeply divided leaves of some Sphenophyllums and those of Archaeocalamites are very similar in form; and the course of the vascular strands in Sphenophyllum may be compared with that in Archaeocalamites. But the striking difference in the structure of the stele forms a wide gap between the two genera. We have evidence that the Calamites and Sphenophyllums were probably descended from a common ancestral stock, and it may be that in Archaeocalamites, some of the Sphenophyllum characters have been retained; but there is no close affinity between the two plants.

On the whole, considering the age of Archaeocalamites and the few characters with which we are acquainted, it is probable that this genus is very closely related to the typical Calamites, and may be regarded as a type which is in the direct line of development of the more modern Calamite and the living Equisetum. Weiss[859] includes Archaeocalamites as one of his subgenera with Calamitina and others, and it is quite possible that the genus has not more claim to stand alone than other forms at present included in the comprehensive genus Calamites.

The student will find detailed descriptions of this genus in the works which have been referred to in the preceding pages.