"Before leaving these curious specimens of ancient skin, the most ancient I suppose known to exist, it is of interest to observe that the thicker portions, when broken across, have the aspect of jet, or of pure shining coal, and thin slices, under the microscope, have the same rich brown colour with that material, though rather more translucent. When burned, fragments of the substance give a strong flame, and a bituminous and ammoniacal odour. We have thus an example of the production of coal from animal membrane, no doubt gelatinous and horny in the first instance, but which has proved itself capable of the same chemical changes that have been experienced by the vegetable matter buried with it. In order that this substance should be preserved in this way, it would be necessary that it should either be kept dry and hard, or that it should be immediately buried in matter impervious to air and kept moist. The latter conditions are the more probable. The preservative qualities of the peaty vegetable matter imbedded with it must be considered; and it is possible that these hollow stumps, partly filled with fragments of _Sigillaria_ bark, may have formed natural tan-pits, in which animal membranes would be preserved in a manner impossible in ordinary sediments. If this were the case, we may yet find an entire reptile, preserved as a flattened mummy, in one of these strange repositories." =Genus PLATYSTEGOS Dawson, 1895.= Dawson, Proc. and Trans. Roy. Soc. Canada, 1895, XII, p. 77 (sec. IV). Type: _Platystegos loricatum_ Dawson. Dawson's description is as follows: "Head broad and short, orbits very large, cranial bones deeply sculptured; teeth strongly plicated and curved, with sharp edges at apices, especially the inner palatal teeth, which are very large. Many minute teeth on the vomerine bones; vertebræ ossified, biconcave; limb bones imperfectly ossified, short; lower surface protected with a thoracic plate and thick, densely imbricated bony scales in transverse rows; body above with thin, round scales, concentrically marked." =Platystegos loricatum Dawson.= Dawson, Proc. and Trans. Roy. Soc. Canada, XII, p. 77, 1895. Dawson describes the species: "Head about 8 cm. long; when flattened 9 cm. broad across parietal foramen; squamosal and temporal bones projecting backwards in points much behind the condyles; parietal foramen small, orbits large; length of longest tooth seen 7 mm.; cranial bones closely and deeply pitted; humerus with very thin bony walls, cartilaginous within, 3.5 cm. long." Erect tree, coal formation, at the South Joggins; collected by P. W. McNaughton. Type in Peter Redpath Museum at McGill University. Dawson regarded the form as of uncertain relationship. CHAPTER XXV. THE STEREOSPONDYLOUS AMPHIBIA FROM THE COAL MEASURES OF NORTH AMERICA. DEFINITION OF THE ORDER STEREOSPONDYLIA ZITTEL, 1887.