54 
Scott. — On a Palaeozoic Fern , the 
aphlebia-strands. In the latter, these bundles, as they pass out through the 
cortex, become, as we have seen, much flattened and tangentially extended 
(PI. Ill, Fig. 6). The second Williamson specimen shows nothing of the 
kind ; the aphlebia-strands are only slightly elliptical in section, however 
far out in the cortex they may be. It is possible that the difference may be 
exaggerated by accidents of preservation, the strands in the Shore plant 
having to some extent collapsed, but a real distinction, though probably 
not an important one, certainly remains. 
The Williamson type-specimens of 1888 agree in this respect, as in 
others, with the Shore fossil. The preservation of the cortex is very 
imperfect ; the parts that persist are generally the external margin, the 
inner margin of the outer cortex, and a margin round the various outgoing 
strands, including those of the aphlebiae (PI. II, Phot. 15). It is, however, 
evident that the aphlebia-strands are much flattened in the outer part of 
their course. 
The type-specimens appear to be of the same variety or form as the 
Shore fossil, though the former came from a roof-nodule and the latter 
from a seam-nodule. The largest stem in the type is about 22 mm. in 
diameter, with the wood measuring 6 mm. The form of the stele agrees 
very closely (compare PI. I, Phots. 1-6, with PI. II, Phot. 15); as we have 
seen, crescentic leaf-traces occur in both and the aphlebia-strands are alike. 
There can be no doubt on the evidence that the new specimen belongs to 
the true Zygopteris Grayi, as founded by Williamson on the 1888 specimens. 
His later specimen, as we have seen, is a little different in detail, but not, 
as it seems to me, sufficiently so to warrant specific distinction. 
Williamson’s later specimen shows some points of interest as regards 
the axillary stele. The mode of separation between this stele and the foliar 
bundle is rather different from that shown in the Shore plant. In the latter, 
as we have seen, the undivided trace is a massive structure, and when the 
adaxial bulge is to be cut off as the axillary stele the line of separation simply 
passes through the thick band of the abaxial xylem (PI. I, Phot. 1,/./., a.s.). 
In the other, the xylem is narrow and has to be thickened up by the addition 
of more tracheides, before separation can take place (Kidston, TO, p. 452 ; 
PL XXXIV, Figs. 3 and 4). Thus the formation of a gap in the xylem- 
band is avoided. Further, the axillary stele bears a much larger proportion 
to the foliar bundle at the point of separation than in the Shore plant. 
The stele and bundle a little above their severance are shown in Fig. 13, 
PI. V. The structure of the stele is the same as at the corresponding level 
in the Shore specimen, but the phloem is well preserved, forming a ring 
round the xylem, and conspicuous by its large sieve-tubes. So far there is 
no indication of lateral appendages. 
In Phot. 10, PL II, the stele is shown further out in its course, 
where the axillary branch is nearly free. Here the internal xylem is 
