10 T. O. HALLE, LOWER DEVONIAN PLANTS FROM RÖRAGEN IN NORWAY. 



They form an angle of about 70° to the axis of the stem and occur at a distance of about 

 3 — 5 mm. above each other, measured parallel to the axis. There is anotlier less distinct 

 system of much steeper spirals running in the opposite direction. 



C. Specimens w i t h t h i c k, s h o r t (rudimentary or broken) 

 distant leaves (Nathorst, 1. c, pl. 5, fig. 10; this paper; pl. 1, figs. 

 9—20; pl. 4, fig. 5). - - The specimen shown in pl. 1, fig. 9, differs markedly from those 

 already described. It is considerably stouter, and it is also stouter than the stems figured 

 by Dawson. It represents a part of a simple axis, about 17 cm. long and with a maxi- 

 mum breadth of 2 cm. on the impression. The surface of the impression is irregularly 

 wrinkled longitudinally. The leaves are very distant and apparently irregularly placed, 

 though their precise manner of disposition cannot be ascertained. They are best shown 

 at the outlines of the impression, and are there found to be shortly triangulär, with 

 breadth and length about equal, 7 — 8 mm. They are slightly falcate with an acute but 

 short apex. In their natural state, therefore, the leaves ha ve evidently been shortly pyra- 

 midal in shape, passing över gradually into the axis. On the surface of the impression, 

 the leaves — which should there appear as more or less rounded pits — are seen very in- 

 distinctly or not at all. On the counterpart of the specimen figured, however, there are 

 some rounded impressions, which probably represent imprints of the leaves. With the 

 specimen now described agrees closely anotlier fragment of a stem figured by Nathorst 

 (1. c, pl. 5, fig. 10). - These specimens belong to a type which is somewhat different 

 from the typical forms of Arthrostigma gracile figured by Dawson. The difference con- 

 sists chiefly in the fact that the leaves are short, pyramidal and thorn-like and more 

 distantly placed. The identity of the present specimens with those figured by Dawson 

 might therefore be regarded as doubtful. In the latter, however, as well as in the typical 

 forms of Arthrostigma gracile from Röragen described above, under A., the leaf-bases 

 are often found to have a shape similar to that of the structures which we have here 

 described as leaves. A couple of specimens from the Lower Old Red of Scotland showing 

 a very close resemblance to the one in pl. 1, fig. 9, have already been described by Kidston 

 (1. c. ) and have been identified by him with Da\vson's Arthrostigma gracile. Regarding 

 the lateral appendages Kidston (1. c, p. 107) says: »I do not think that these spine- 

 like structures are the bases of leaves, as has been suggested, but are the leaves them- 

 selves, though developed in a very rudimentary form as in Psilophyto?i». The Röragen 

 specimens do not give any additional evidence as to this question: it must be admitted 

 that there is no trace of the missing upper linear part of the leaf. However this may be, 

 there is certainly a striking agreement between the thorn-like appendages in our spe- 

 cimens and in those figured by Kidston on one side and the basal parts of the leaves of 

 typical Arthrostigma on the other. This resemblance is so great that together with the 

 general agreement of these plant-remains it would seem to be a sufficient proof of the 

 specific identity of these two sets of specimens. It is of less importance in this respect 

 whether the upper linear parts of the leaves have fallen off before fossilization or 

 the leaves in some part of the plant are rudimentary, with only their basal parts 

 developed. 



