Branching forms referred to _Licrophycus_ of Billings, and some of those referred to _Buthotrephis_, Hall, as well as radiating markings referable to _Scotolithus_, _Gyrophyllites_, and _Asterophycus_, are explained by the branching burrows of worms illustrated by Nathorst and the author. _Astropolithon_, a singular radiating marking of the Canadian Cambrian,[S] seems to be something organic, but of what nature is uncertain (Fig. 9). [S] Supplement to "Acadian Geology." [Illustration: Fig. 8.--_Palæophycus Beverlyensis_ (Billings), a supposed Cambrian Fucoid, but probably an animal trail.] _Rhabdichnites_ and _Eophyton_ belong to impressions explicable by the trails of drifting sea-weeds, the tail-markings of Crustacea, and the ruts ploughed by bivalve mollusks, and occurring in the Silurian, Erian, and Carboniferous rocks.[T] Among these are the singular bilobate forms described as _Rusophycus_ by Hall, and which are probably burrows or resting-places of crustaceans. The tracks of such animals, when walking, are the jointed impressions known as _Arthrophycus_ and _Crusiana_. I have shown by the mode of occurrence of these, and Nathorst has confirmed this conclusion by elaborate experiments on living animals, that these forms are really trails impressed on soft sediments by animals and mostly by crustaceans. [T] "Canadian Naturalist," 1864. I agree with Dr. Williamson[U] in believing that all or nearly all the forms referred to Crossochorda of Schimper are really animal impressions allied to Nereites, and due either to worms or, as Nathorst has shown to be possible, to small crustaceans. Many impressions of this kind occur in the Silurian beds of the Clinton series in Canada and New York, and are undoubtedly mere markings. [U] "Tracks from Yoredale Rocks," "Manchester Literary and Philosophical Society," 1885. [Illustration: Fig. 9.--_Astropolithon Hindii_, an organism of the Lower Cambrian of Nova Scotia, possibly vegetable.]