1012 
Scott. — The Structure of 
Mr. Maslen has pointed out that ‘ M. Sutcliffii (as well as the other 
species of Mesoxylon ) exhibits structural characters intermediate between 
those of Cordciites and Poroxylon , but on the whole stands much nearer to 
the former genus ’ (Maslen, ’ll, p. 409). 
I think this opinion is justified ; the chief character in which Poroxylon 
is approached is the very definite one of the presence of centripetal wood 
in the stem. It was on this ground that I at first put M. Sutcliffii pro- 
visionally in the genus Poroxylon (Scott, ’ 09 , p. 51 1). As regards most, if 
not all, of the species referred to Mesoxylon , the characters common to 
Cordaites are more numerous, if less important. The relation of our genus 
to certain other genera, recently established, will be briefly considered at 
the close of the paper. 
Mesoxylon Lomaxii, Scott and Maslen. 
The specimens of M. Lomaxii are larger than most of the others. The 
three fragments known at present, which may possibly have come originally 
from a single stem, measure respectively : 
5'5 x 2 '3 cm. (Slide 2325) 
6-° x 3*5 cm. (Slide 2326) 
and 5-ox 4*o cm. (Slides 2327 and 2328). 
These rough measurements are probably rather under the mark, owing to 
the difficulty of allowing accurately for the partial destruction of the 
cortex. 1 
All the specimens are from roof-nodules at Shore, and the preservation 
is of the usual roof-nodule type : much tissue has been lost altogether, but 
the remaining portions are often well preserved, though not remarkably so 
in this case. Fortunately the inner margin of the wood is one of the best 
preserved regions (PL LXXXVII, P'igs. 1 and 2). 
The pith is large : in the least distorted of the specimens (see Fig. 1) 
it measures 22 X 17 mm. in diameter. There is a continuous and persistent 
outer zone of pith, while the central region is in the usual discoid condition 
(PI. LXXXIX, Fig. 17). 
The other striking features of the species are the dense zone of wood, 
with numerous prominences, corresponding no doubt to the position of the 
leaf-traces, on the side towards the pith (Figs. 1 and 2) ; the evident groups 
of centripetal xylem in the primary strands of the wood (PI. LXXXVII, 
1 The longitudinal sections, from the same specimen as the transverse section 2326, are 
numbered 2375-2383. There are five more sections in the Collection at University College, London, 
lent me by Prof. F. W. Oliver, F.R.S. Q 6 m is a transverse section cut immediately above my 
2328, while Q6n, also transverse, belongs to the same fragment as 2326, and was probably cut 
below that section. Q 6 o-Q 6 q are three longitudinal sections cut from the same specimen as my 
transverse section 2325. All the University College sections are good, and of quite equal importance 
to those in my own collection. 
