122 Scientific Proceedings^ Royal Dublin Society. 



(there are signs of five or six at tlie base), and also strengthened by a frame- 

 work of sclerotic plates or bands, running both vertically and horizontally. 

 (Unfortunately, there are no petrified specimens of A. Iiibernka known by 

 which the internal structure can be ascertained.) Every specimen I have seen 

 shows the rectangular reticulate striation, and it seems too deep-seated to be 

 artificial. The presence of a cortical framework seems necessitated by the 

 size of the frond, and the apparently small development of vascular tissue 

 in the rachis. Though the primary rachis has not, so far, been found 

 bifurcated, I have seen several cases in which the secondary rachis (i.e. the 

 rachis of the pinnae) shows dicliotomy — a feature common to so many 

 Palaeozoic plants, but not hitherto observed in Archseopteris, except by 

 Nathorst in A.Ji.ssih's, where some doubt is expressed by him as to its actual 

 occurrence. These cases in A. hibernica are so clear and relatively frequent 

 that dichotomy of the main rachis merely awaits discovery, I think. It is 

 on account of unobserved dichotomy in the frond of Archaeopteris that 

 Seward would exclude from it A. Tschermald and A. Daicsoni, described by 

 Stur from the Culm of Altendorf. If the identification of the fertile 

 specimen from Kiltorcan as A. Tschermald, Stur is correct,' then any doubt 

 as to dichotomy in Archseopteris is removed, as Stur describes and figures 

 dichotomy in this species. 



3. Pinnce. — The pinnae are two-ranked and generally opposite, though alter- 

 nation occurs in some specimens. Each pinna is occasionally placed at right 

 angles to the rachis, but usually forms a wide acute angle of 70°-80° with it, 

 and carries on its own (secondary) rachis ten to twelve pairs of imbricate 

 pinnules. The pinnae are attached to the primary rachis at intervals of 

 4 cm., and touch one another above and below by the edges of their pinnules. 

 The pinna is elongated and oblong in outline, and may be 30 cm. long 

 and nearly 5 em. wide (25 x 4 cm. is an average size). Each pinnule 

 (2'5 X 1'5 em.) is asymmetrical, oblong-obovate in outline, and attached by 

 a narrow wedge-shaped decurrent base to the secondary rachis. The pinnules 

 are usually imbricate, and not distinctly stalked. Their margin is entire, 

 slightly toothed, or even somewhat lobed. Each pinnule is traversed by 

 numerous sub-parallel veins, which reach the margin 0'5 mm. apart from 

 one another, and may give rise by tlieir projections to a toothed edge. They 

 enter the pinnule from the rachis as three or four distinct bundles, and as 

 they pass to its edge undergo bifurcation or dichotomy several times, tlms 

 giving the numerous bundles observable. There is no suggestion of a midrib or 

 median nerve, and the three or four bundles can be seen clearly entering the 



1 Scient. Proc. Roy. Dub. Soc, 1911, vol xiii, p. 137. 



