KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 51. N:o |0. 9 
proximal one convex; apex rounded or acute. Venation generally rather distinct, 
consisting of several forked, radiating or parallel veins, which come direct from the 
rachis. Consistence firm. 
The cuticle (pl. 3, figs. 7—9) has been examined in several specimens, and on 
the whole presents the same structure, though the thickness, the number of the 
stomata, and the degree of the differentiation above the veins are subject to a cer- 
tain variation. It is thick and firm, and composed of irregularly to isodiametrically 
polygonal cells. The tissue of the upper epidermis is uniform, and generally lacks 
stomata altogether. The lower cuticle is somewhat thinner, and has more or less dis- 
tincet strips of oblong cells indicating the course of the veins. Between the latter 
there are numerous stomata (pl. 3, fig. 9) of the structure (pl. 1, fig. 7) stated above 
(p. 4). Sometimes the epidermis has rounded holes (pl. 3, fig. 7), the appearance 
and the occurrence of which I have already described (p. 4). 
When NATHORST instituted this species, there were only a few specimens at 
his disposal, and for this reason he gave it a somewhat narrow delimitation. It was 
principally characterized by falcate, obtuse and imbricate pinnae and by dense, dis- 
tinet, forked, radiating veins. At the same time he instituted a var. longior, which, 
however, I have withdrawn, because the use of varieties does not appear appropriate 
in the case of fossil plants. 
The following year NATHORST (1879, p. 63) described a new species, Ptilo- 
zamites falcatus, which in his opinion at that time was distinguished from Pt. Nils- 
sont by sparser, less radiating veins and by the pinnae not being imbricate. Later 
on, however (1886, p. 123), he observed that Pt. Nilssonmi has not always imbricate 
pinnae. Herewith the last supposed difference disappeared. 
Some fragments originally described as Ctenopteris? falcata NATH. (1878, p. 62) 
Prof. NATHORST soon after (1880, p. 66) placed under Ptilozamites falcatus. 
When NATHORST described the fossils in question, there stood out certain types 
of frond which could possibly be regarded as different species, though not so well 
distinguished; but as the collection has increased, the gaps have been filled. At 
present the series is so complete that I have felt obliged to include in Pt. Nilssonti 
not only Pt. falcatus (incl. Ctenopteris? falcata) — although probably not the in- 
determinable pl. 10, fig. 1, NATHORST 1878 — but also a great number of considerably 
varying fronds which have not previously been described. Some types can, it is 
true, be distinguished, but these always merge into each other, and therefore, if 
one tries to characterize them, it always proves impossible to do so. — I have already 
spoken of the differences between Pt. Nilssoni and Pt. falcatus according to NATHORST. 
Though the original specimens present a certain difference, yet this is of but 
little importance. As is well known, the venation is always subject to a certain 
variation, and otherwise its varying distincetness in the present specimens seems to 
a great extent due to the mode of preservation. 
As has just been mentioned, the veins are sometimes very strong, and sometimes 
rather indistinct; but as a rule they are something between these two extremes (pl. 1, figs. 
EK. Sv. Vet. Akad. Handl. Band 51. N:o 10 2 
