The plants described by these gentlemen from the Old Red Sandstone of Callender, I should suppose, from their figures and descriptions, to belong to the genus _Arthrostigma_, rather than to Psilophyton. I do not attach any importance to the suggestions referred to by them, that the apparent leaves may be leaf-bases. Long leaf-bases, like those characteristic of _Lepidofloyos_, do not occur in these humbler plants of the Devonian. The stems with delicate "horizontal processes" to which they refer may belong to _Ptilophyton_ or to _Pinnularia_. In conclusion, I need scarcely say that I do not share in the doubts expressed by some British palæontologists as to the distinctness of the Devonian and Carboniferous floras. In eastern America, where these formations are mutually unconformable, there is, of course, less room for doubt than in Ireland and in western America, where they are stratigraphically continuous. Still, in passing from the one to the other, the species are for the most part different, and new generic forms are met with, and, as I have elsewhere shown, the physical conditions of the two periods were essentially different.[BW] [BW] "Reports on Devonian Plants and Lower Carboniferous Plants of Canada." It is, however, to be observed that since--as Stur and others have shown--_Calamities radiatus_, and other forms distinctively Devonian in America, occur in Europe in the Lower Carboniferous, it is not unlikely that the Devonian flora, like that of the Tertiary, appeared earlier in America. It is also probable, as I have shown in the "Reports" already referred to, that it appeared earlier in the Arctic than in the temperate zone. Hence an Arctic or American flora, really Devonian, may readily be mistaken for Lower Carboniferous by a botanist basing his calculations on the fossils of temperate Europe. Even in America itself, it would appear, from recent discoveries in Virginia and Ohio, that certain Devonian forms lingered longer in those regions than farther to the northeast;[BX] and it would not be surprising if similar plants occurred in later beds in Devonshire or in the south of Europe than in Scotland. Still, these facts, properly understood, do not invalidate the evidence of fossil plants as to geological age, though errors arising from the neglect of them are still current. [BX] Andrews, "Palæontology of Ohio," vol. ii.; Meek, "Fossil Plants from Western Virginia," Philosophical Society, Washington, 1875. VI.--Geological Relations of some Plant-bearing Beds of Eastern Canada. ("Report on Erian Plants," 1871.)