The macrospores above referred to may have belonged to humble aquatic plants mantling the surfaces of water or growing up from the bottom, and presenting little aërial vegetation. But there are other Erian plants, as already mentioned, which, while of higher structure, may be of Rhizocarpean affinities. One of these is the beautiful plant with whorls of wedge-shaped leaves, to which the name _Sphenophyllum_ (see Fig. 20) has been given. Plants referred to this genus have been described by Lesquereux from the upper part of the Siluro-Cambrian,[AP] and a beautiful little species occurs in the Erian shales of St. John, New Brunswick.[AQ] The genus is also continued, and is still more abundant, in the Carboniferous. Many years ago I observed, in a beautiful specimen collected by Sir W. E. Logan, in New Brunswick, that the stem of this plant had an axis of reticulated and scalariform vessels, and an outer bark.[AR] Renault and Williamson have more recently obtained more perfect specimens, and the former has figured a remarkably complex triangular axis, containing punctate and barred vessels, and larger punctate vessels filling in its angles. Outside of this there is a cellular inner bark, and this is surrounded by a thick fibrous envelope. That a structure so complex should belong to a plant so humble in its affinities is one of the strange anomalies presented by the old world, and of which we shall find many similar instances. The fruit of _Sphenophyllum_ was borne in spikes, with little whorls of bracts or rudimentary leaves bearing round sporocarps. [AP] "American Journal of Science." [AQ] Dawson, "Report on Devonian Plants," 1870. [AR] "Journal of the Geological Society," 1865. [Illustration: Fig. 17.--_Ptilophyton plumosum_ (Lower Carboniferous, Nova Scotia). Natural size and magnified.] A second type of plant, which may have been Rhizocarpean in its affinities, is that to which I have given the name _Ptilophyton_.[AS] It consists of beautiful feathery fronds, apparently bearing on parts of the main stem or petiole small rounded sporocarps. They are found abundantly in the Middle Erian of the State of New York, and also occur in Scotland, while one species appears to occur in Nova Scotia, as high as the Lower Carboniferous (Figs. 17, 18). [AS] _Plumalina_ of Hall. [Illustration: Fig. 18.--_Ptilophyton Thomsoni_ (Scotland), _a_, Impression of plant in vernation, _b_, Branches conjecturally restored, _c_, Branches of _Lycopodites Milleri_, on same slab.] These organisms have been variously referred to Lycopods, to Algæ, or to Zoöphytes, but an extended comparison of American and Scottish specimens has led me to the belief that they were aquatic plants, more likely to have been allied to Rhizocarps than to any other group. Some evidence of this will be given in a note appended to this chapter.