ioi7 
Mesoxylon Lomctxii and M. poroxyloides. 
Pith large and discoid, with a persistent outer zone. 
Twin-bundles of the leaf- trace converging rapidly in the wood, and 
fusing immediately on reaching the edge of the pith. 
Centripetal xylem well developed, persisting for a long distance below 
the fusion of the twin-bundles. 
Xylem-strands at the margin of the pith with a distinct and wide 
sheath in the upper part of their course. 
Spiral and scalariform tracheides constituting the whole of the leaf- 
trace xylem and the inner part of the corresponding secondary wood, but 
almost absent from the intermediate secondary wood. 
Bordered pits in two or three rows. 
Medullary rays (with rare exceptions) uniseriate, 1-25 cells in height. 
Secondary inner cortex or periderm of great thickness. 1 
Dictyoxylon zone relatively narrow. 
Roof-nodules ; Shore, Littleborough. Lower Coal Measures. 
This species is named after Mr. James Lomax, to whom its discovery 
and that of the other species of Mesoxylon is due. 
Mesoxylon poroxyloides, Scott and Maslen. 
This species, like the last, was first named and shortly described in 
1910, in the joint Note by Mr. Maslen and myself. It had, however, already 
been referred to, together with M. multirame , in the second edition of my 
‘Studies in Fossil Botany’ (Scott, ’ 09 , p. 52 6), where I mentioned the 
occurrence of stems from Shore, in which the centripetal wood of a Poroxylon 
co-existed with the discoid pith and other characters of a Cordaites. 
Mesoxylon poroxyloides is a fossil from the ordinary coal-balls or seam- 
nodules of Shore ; in this respect it is like M. multirame , and differs from 
M. Sntcliffii , M, Lomaxii , and M. pi aiy podium, which are all roof-nodule 
specimens. The preservation of M. poroxyloides is consequently more 
complete than that of the species last mentioned, for it is free from the 
patchiness which is the peculiar defect of specimens from the roof-nodules. 
The detailed investigation has been carried out on one specimen, represented 
in my collection by seven sections (slides 2352-2358), of which four are 
transverse and three longitudinal. This may be called the type specimen. 2 
1 This character must, of course, vary with the age of the specimen. 
2 There are six more sections of this specimen in the University College collection, for the loan 
of which I am indebted to my friend Prof. F. W. Oliver, F.R.S. Two of the sections, Q 6 a and 
Q6b, are transverse, and four, Q6c-Q6f, longitudinal. I have been able to determine the order 
of four of the transverse sections, which, from below upwards, run thus : 
S. Coll. 2352 
»> 2353 
Univ. Ccrll. Coll. 06 a 
?? Q 6 b 
The other two transverse set tions are not in series with the above, but 2355 comes below 2354. 
