10 ERNST ANTEVS, THE SWEDISH SPECIES OF PTILOZAMITES NATH. 
2, 4, 5; pl. 3, fig. 6). Nor do they always radiate, but they are by no means rarely 
parallel. Finally, they are sometimes dense, and sometimes sparse. 
The segments are generally rather short and broad with a rounded apex, but 
they may vary somewhat in appearance. In some fronds (pl. 2, fig. 8) they are fal- 
cate, pointing upwards, and narrowing towards the apex. These pinnae differ more 
than any others from the typical ones, but the transition to them is fully complete, 
no link being missing. 
NATHORST (1878 a, p. 23) tried to fix certain limits regarding size, and thus 
instituted a variety longior. It is not easy, however, to fix such limits, for this 
type of frond is found in quite small fronds (pl. 1, fig. 3) as well as in compara- 
tively large ones (pl. 3. fig. 4), and between these extremes there are all sizes. These 
differences may often depend on the age of the specimens, but perhaps not always. 
I have examined the cuticle in fronds of all sizes, but I have never found that the 
small fronds have a thinner cuticle than the large ones, as might be expected if 
they were very young. Several explanations are possible. The fronds here grouped 
together possibly belonged to different botanical species; they may have had a differ- 
ent position on the stem; and, finally, all specimens of one and the same species 
do not attain: the same size. 
Taken in this sense, the species is well delimited against others of the same 
genus. The only one which can be compared to it is Ptilozamites fallax NATH., to 
which some forms with long pinnae show a not inconsiderable resemblance. Re- 
garding the difference between these two species reference may be made to the 
treatment of Pt. fallax (p. 11). 
From species of other genera Pt. Nilssoni is well distinguished by the bifurca- 
tion of the rachis, combined with the shape and the venation of the pinnae. 
Pt. Nilssomi is represented by a large and fine collection from different locali- 
ties in Scania. It was first described from the lower seam at Höganäs, where it 
occurs principally in the ferrugineous claystone, but also, though more rarely, in the 
black slate. The greater part of the collection was found in the plant-bearing layer 
a at Bjuf, and a smaller number of specimens are from Bjuf 1, 3, 4, and the lower 
seams at Skromberga and Hyllinge. All the deposits in which Pt. Nilssoni occurs 
belong to the Rhaetic. (Bjuf 2, zone with Dictyophyllum exile. Höganäs, Skrom- 
berga, and Hyllinge the lower seams, and Bjuf 1—3, zone with Camptopteris spi- 
ralis. Bjuf 4, zone with Lepidopteris Ottonis.) 
Ptilozamites fallax Narr. 
123 [SJ HS a a I OS Sa LR tf | 
Ptilozamites fallax, NATHoORST 1878 a, pp. 7, 24; pl. 3, fig. 18. 
» » NATHORST 1878, p. 11. 
» > CC NATHORST 1879, Pp. O96 PlEcd Hg.eLÖS 
» » NATHORST 1880, p. 66. 
» » NATHoRST 1886, p. 122. 
