4 Seward . — On the genus Myeloxylon (. Brong .). 
been made use of by Renault as a basis of classification : in 
one type, Myelopteris Landriotii , the fibrous bundles of the 
hypoderm are circular, elliptical, or reniform ; in the second 
type, M. radiata , they are flattened and arranged as radiating 
bands of sclerenchymatous tissue. Our English specimens 
agree more closely with the M. radiata type. Whilst ad- 
mitting a few points of difference between Myelopteris and 
recent Ferns, Renault concludes that its true position is with 
the Marattiaceae. One of the arguments considered by him of 
great weight in favour of this decision is the common associa- 
tion of Alethopteris- leaflets and Myelopteris- petioles ; and in 
one case a rachis of Alethopteris aquilina is figured showing the 
same structure as that of Myelopteris. The force of this and 
other arguments will be considered at the conclusion of these 
notes. Before passing on to Williamson’s description of 
Myeloxylon , I may briefly refer to a specimen in the British 
Museum collection 1 which throws a little more light on the 
structure of the vascular bundles. This specimen, unfor- 
tunately with no record of locality, came in all probability 
from one of the places from which Renault’s silicified speci- 
mens were obtained : its general structure and mode of 
preservation strongly support this view. In Fig. i, where I 
have represented one bundle and two canals, a number of 
thick-walled elements are clearly shown at ^ in contact with 
the xylem, and at p what we may probably consider as one of 
the protoxylem-tracheids. In the space next to the pro- 
toxylem are traces of torn and delicate tissue (a), no doubt 
remnants of phloem : surrounding the phloem half of the 
bundle is a sheath of small parenchymatous cells. 
In his seventh memoir 2 on the Organization of the fossil 
plants of the Coal-measures, Prof. Williamson gives some 
account of the history of Myelopteris and describes a number 
of specimens from the English Coal-measures. In these 
1 For access to specimens in the British Museum my thanks are due to 
Mr. Carruthers. 
2 Williamson, On the organization of the fossil plants of the Coal-measures, 
Pt. VII. Phil. Trans. Royal Society, 1876. 
