Using Calamites as a generic name for all those Calamarian stems in which the ribs alternate at the nodes, we have, on Weiss's system, the following sub-genera: Stylocalamites, branches rare and irregularly arranged; Calamitina, branches in regular verticils, limited to certain nodes, which surmount specially short internodes; Eucalamites, branches present on every node.
Here, as in the previous genus, sterile and fertile verticils are ranged alternately on the axis of the cone.
Weiss first showed, immediately below the verticils of bracts, the position thus being the reverse of that in Palaeostachya.
Which in structure resembles the vegetative stem in its primary condition, bears numerous verticils of bracts, those of each verticil being coherent in their lower part, so as to form a disc or cup, from the margin of which the free limbs of the bracts arise.
In diameter; the stout axis bears numerous whorls of compound sporophylls, the members of successive verticils being superposed.