6 T. G. HALLE, L0VER DEVONIAN PLANTS FROM RÖRAGEN IN NORWAY. 



feature of a certain interest in regard to the conditions under Avliich tlie plants were pre- 

 served is the occurrence of tracks of worms or some other animals on the bedding planes, 

 as shown in text-fig. 1. 



The plant-remains usually occur only as impressions without any traces of the 

 original substance. Sometimes, however, the latter is preserved in a carbonized state; 

 and in such specimens resistant parts of the plants, such as tracheids and spores, can be 

 examined after treatment with Schultze's mixture in the usual way. In other cases the 

 original tissue is replaced by a greenish grey substance, which according to Prof. Gold- 

 schmidt probably is chloritic, or more of ten by pyrites or hydroxide of iron. In excep- 

 tional cases some ferruginous matter has penetrated and partly petrified the tissue. Con- 

 sidering the age of the rocks, the preservation of the plant-remains on the whole must 

 be stated to be fairly good. There is a certain difference in regard to the preservation 

 between the plant-remains in the sandstone and those in the finer-grained slate. In the 

 former the impressions appear in a deeper relief more suggestive of the original shape 

 of the part in question, whereas the finer details are not well shown on the coarse rock. 

 In the slate the impressions are much more flattened, but the finer details are 

 very well shown. In the plates accompanying this paper are shown several instances 

 of the preservation of minute structures which prove that the state in which the plant- 

 remains present themselves for examination is not an unfavourable one. — The exa- 

 mination of the impressions is often impeded by the thick rust-covering foimd on many 

 of the slabs. In such cases it is convenient to remove the rust by means of a momentary 

 washing of the surface with warm fluoric acid after which the slab is immediately placed 

 in water. This method, which was introduced by Prof. Goldschmedt, has proved a 

 great help. 



Description of species. 

 Arthrostigma gracile Daws. — Pl. 1, figs. 1 — 20; pl. 4, figs. 1—5. 



? Drepanophycua spinacformis, Göppert 1852; p. 92; pl. 41, fig. 1. 



Arthrostigma gracile, Dawson 1871; p. 41; pl. 13. 



? Psilophyton princeps var. ornatum Daws., pars, Dawson 1871; pl. 10, fig- 111; [not the other specimens figured 



under the same name]. 

 Psilophyton ? sp., Jack & Etheridge 1877; p. 217; figs. 1, 2. 

 Arthrostigma gracile Daws., Dawson 1882 a; p. 104; [not pl. 24, fig. 22]. 

 Arthrostigma gracile Daws., Kidston 1893; p. 102; pl. 3. 

 Specimens compared by Nathorst, 1913, pp. 26 — 27, with Psilophyton spinosum and bohemicum (pl. 4, figs. 8,9) 



and with Drepanophycus and Arthrostigma (pl. 5, figs. 10, 11). 



Historical. 



The genus Arthrostigma was instituted by Dawson in 1871 for some stem-like 

 impressions from the well-known plant-bearing beds at Gaspé in eastern Canada. Dawson 



