[CX] See "Memoirs of Dr. Williamson," in "Philosophical Transactions," for ample details.
As a type of Lepidodendron, I may describe one of the oldest Carboniferous species characteristic of the Lower Carboniferous in America, and corresponding to _L. Veltheimianum_ of Europe.
Lepidodendron Corrugatum, Dawson.--(See Fig. 43, _supra_.) "Quarterly Journal of Geological Society," vol. xv.; "Acadian Geology," page 451.
_Habit of Growth._--Somewhat slender, with long branches and long, slender leaves having a tendency to become horizontal or drooping.
_Markings of Stem._--Leaf-bases disposed in quincunx or spirally, elongate, ovate, acute at both ends, but more acute and slightly oblique at the lower end; most prominent in the upper third, and with a slight vertical ridge. Leaf-scars small, rounded, and showing only a single punctiform vascular scar. The leaf-scar on the outer surface is in the upper third of the base; but the obliquity of the vascular bundle causes it to be nearly central on the inside of the epidermis. In young succulent shoots the leaf-scars are contiguous and round as in Cyclostigma, without distinct leaf-bases. In this state it closely resembles _L. Olivieri_, Eichwald.[CY]
[CY] Lethæa Rossica, Plate Y, Figs. 12, 13.
In the ordinary young branches the leaf-scars are contiguous, and closely resemble those of _L. elegans_, Brongt. (Fig. 43 C). As the branches increase in diameter the leaf-scars slightly enlarge and sometimes assume a verticillate appearance (Fig. 43 D). As they still further enlarge they become separated by gradually increasing spaces of bark, marked with many waving striæ or wrinkles (Fig. 43 I, N). At the base of old stems the bark assumes a generally wrinkled appearance without distinct scars.
_Knorria or Decorticated States._--Of these there is a great variety, depending on the state of preservation, and the particular longitudinal ridges. Fig. 43 D shows a form in which the vascular bundles appear as cylindrical truncate projections. Other forms show the leaf-bases prominent, or have an appearance of longitudinal ribbing produced by the expansion of the bark.
_Structure of Stem._--This is not perfectly preserved in any of my specimens, but one flattened specimen shows a central medulla with a narrow ring of scalariform vessels surrounding it, and constituting the woody axis. The structure is thus similar to that of _L. Harcourtii_, which I regard as probably the same with the closely allied European species L. Veltheimianum.