Fig. 13.—Buthotrephis Grantii, a genuine Alga from the Silurian, Canada.
The species Buthotrephis subnodosa and B. flexuosa, from the Utica shale, are also certainly plants, though it is possible, if their structures and fruit were known, some of these might be referred to different genera. All of these plants have either carbonaceous matter or produce organic stains on the matrix.
The organism with diverging wedge-shaped fronds, described by Hall as Sphenothallus angustifolius, is also a plant. Fine specimens, in the collection of the Geological Survey of Canada, show distinct evidence of the organic character of the wedge-shaped fronds. It is from the Utica shale, and elsewhere in the Siluro-Cambrian. It is just possible, as suggested by Hall, that this plant may be of higher rank than the Algæ.
The genus Palæophycus of Hall includes a great variety of uncertain objects, of which only a few are probably true Algæ. I have specimens of fragments similar to his P. virgatus, which show distinct carbonaceous films, and others from the Quebec group, which seem to be cylindrical tubes now flattened, and which have contained spindle-shaped sporangia of large size. Tortuous and curved flattened stems, or fronds, from the Upper Silurian limestone of Gaspé, also show organic matter.
Respecting the forms referred to Licrophycus by Billings, containing stems or semi-cylindrical markings springing from a common base, I have been in great doubt. I have not seen any specimens containing unequivocal organic matter, and am inclined to think that most of them, if not the whole, are casts of worm-burrows, with trails radiating from them.
Though I have confined myself in this notice to plants, or supposed plants, of the Lower Palæozoic, it may be well to mention the remarkable Cauda-Galli fucoids, referred by Hall to the genus Spirophyton, and which are characteristic of the oldest Erian beds. The specimens which I have seen from New York, from Gaspé, and from Brazil, leave no doubt in my mind that these were really marine plants, and that the form of a spiral frond, assigned to them by Hall, is perfectly correct. They must have been very abundant and very graceful plants of the early Erian, immediately after the close of the Silurian period.
We come now to notice certain organisms referred to Algæ, and which are either of animal origin, or are of higher grade than the sea-weeds. We have already discussed the questions relating to Prototaxites. Drepanophycus, of Goeppert,[AB] I suspect, is only a badly preserved branch or stem of the Erian land-plant known as Arthrostigma. In like manner, Haliserites Dechenianus,[AC] of Goeppert, is evidently the land-plant known as Psilophyton. Sphærococcites dentatus and S. serra—the Fucoides dentatus and serra of Brongniart, from Quebec—are graptolites of two species quite common there.[AD] Dictyophyton and Uphantenia, as described by Hall and the author, are now known to be sponges. They have become Dictyospongiæ. The curious and very ancient; fossils referred by Forbes to the genus Oldhamia are perhaps still subject to doubt, but are usually regarded as Zoöphytes, though it is quite possible they may be plants. Though I have not seen the specimens, I have no doubt whatever that the plants, or the greater part of them, from the Silurian of Bohemia, described by Stur as Algæ and Characeæ,[AE] are really land-plants, some of them of the genus Psilophyton. I may say in this connection that specimens of flattened Psilophyton and Arthrostigma, in the Upper Silurian and Erian of Gaspé, would probably have been referred to Algæ, but for the fact that in some of them the axis of barred vessels is preserved.
[AB] “Fossile Flora,” 1852, p. 92, Table xli.
[AC] Ibid., p. 88, Table ii.