The following are North American species:
| Trunks. | |||
| Dadoxylon Ouangondianum, Dn. | M. Erian | Report, 1871.[CP] | |
| D. Halli, Dn. | ” | ” | |
| D. Newberryi, Dn. | ” | ” | |
| D. Clarkii, Dn. (Cordæoxylon ?) | ” | Report, 1882. | |
| D. Acadianum, Dn. | Coal-formation and millstone grit. | Acadian Geology. | |
| D. Materiarum, Dn. | Do. and Permo-Carb. | ” | |
| D. (Palæoxylon) antiquius, Dn. | L. Carboniferous. | ” | |
| D. annulatum, Dn. | Coal-formation. | ” | |
| Ormoxylon Erianum, Dn. | Erian. | Report, 1871. | |
| Foliage. | |||
| Araucarites gracilis, Dn. | N. Coal-formation and Permian. | ” | |
| Walchia robusta, Dn. | Permian. |  | Report on Prince Edward Island. |
| W. imbricatula, Dn. | ” | ||
[CP] “Geological Survey of Canada: Fossil Plants of Erian and Upper Silurian Formations,” by J. W. Dawson.
All of the above can be vouched for as good species based upon microscopic examination of a very large number of trunks from different parts of North America. The three Erian species of Dadoxylon and D. antiquius from the Lower Carboniferous have two or more rows of cells in the medullary rays. The last named has several rows, and is a true Palæoxylon allied to D. Withami of Great Britain. D. materiarium is specially characteristic of the upper coal-formation and Permian, and to it must belong one or both of the species of foliage indicated above. D. Clarkii has very short, simple medullary rays of only a few cells superimposed, and has an inner cylinder of scalariform vessels, approaching in these points to Cordaites. Ormoxylon has a very peculiar articulated pith and simple medullary rays.
Witham in 1833 described several Carboniferous species of pine-wood, under the generic name Pinites, separating under the name Pitus species which appeared to have the discs on the cell-walls separate and in transverse lines. Witham’s name was changed by Goeppert to Araucarites, to indicate the similarity of these woods to Araucaria, Pinites being reserved for trees more closely allied to the ordinary pines. Endlicher, restricting Araucarites to foliage, etc., of Araucaria-like trees, gave the name Dadoxylon to the wood; and this, through Unger’s “Genera and Species,” has gained somewhat general acceptance. Endlicher also gave the name Pissadendron to the species which Witham had called Pitus; but Brongniart proposed the name Palæoxylon to include all the species with thick and complex medullary rays, whatever the arrangement of the discs. In Schimper’s new work Kraus substitutes Araucarioxylon for Endlicher’s Dadoxylon, and includes under Pissadendron all the species placed by Brongniart in Palæoxylon.
To understand all this confusion, it may be observed that the characters available in the determination of Palæozoic coniferous wood are chiefly the form and arrangement of the wood-cells, the character of the bordered pores or discs of their walls, and the form and composition of the medullary rays.
The character on which Witham separated his genus Pitus from Pinites is, as I have ascertained by examination of slices of one of his original specimens kindly presented to me by Mr. Sanderson, of Edinburgh, dependent on state of preservation, the imperfectly preserved discs or areolations of the walls of the fibre presenting the appearance of separate and distinct circles, while in other parts of the same specimens these discs are seen to be contiguous and to assume hexagonal forms, so that in this respect they do not really differ from the ordinary species of Dadoxylon. The true character for subdividing those species which are especially characteristic of the Carboniferous, is the composite structure of the medullary rays, which are thick and composed of several radial piles of cells placed side by side. This was the character employed by Brongniart in separating the genus Palæoxylon, though he might with convenience have retained Witham’s name, merely transferring to the genus the species of Witham’s Pinites which have complex medullary rays. The Erian rocks present the greatest variety of types, and Palæoxylon is especially characteristic of the Lower Carboniferous, while species of Dadoxylon with two rows of bordered pores and simple medullary rays are especially plentiful in the upper coal-formation and Permo-Carboniferous.
The following table will clearly show the distinctive characters and relations of the genera in question, as held by the several authors above referred to:
Wood of Palæozoic Conifers.