36 
“ On the Structure of an undescribed type of Calamo- 
dendron from the upper Coal-Measures of Lancashire/’ by 
Professor W. C. Williamson, F.R.S. 
The Author called the attention of the Society to the 
structure of the Calamite from the Upper Coal-measures 
represented in Fig. 478 of the 5th edition of Lyell’s Manual 
of Geology. He pointed out the existence of one Calamite 
within another, the former representing the pith and the 
latter the exterior of the bark, the pith and bark being 
separated by a well defined woody zone. This woody zone 
consists of a series of tissues radiating, as in the recent 
conifera, from the pith to the bark ; but instead of being all 
alike, they consist of two structures which are arranged in 
alternating wedges. One of these is entirely composed of 
elongated cells, but which, being arranged in linear rows 
radiating from pith to bark, and being separated from the 
former by a defined line, this tissue is to be regarded as a 
modified form of pleurenchyma rather than of parenchyma. 
The intermediate radiating laminae or wedges resemble slices 
cut out of a coniferous Dadoxylon, having the same reticu- 
lated fibres and muriform medullary rays, the latter con- 
sisting of a single vertical row of cells. These structures 
replace corresponding wedges in the Catamites recently de- 
scribed by E. W. Binney, Esq., but in which latter the wedges 
consist wholly of masses of scalariform tissue unfurnished 
with medullary rays. Immediately below each node Prof. 
Williamson pointed out the existence of a verticil of pro- 
longations of the pith, penetrating the cellular wedges of 
the woody layer like the spokes of a wheel. These he 
terms “ verticillate medullary radii,” to distinguish them 
from the ordinary medullary rays of the fibrous wedges. 
These fibrous and cellular . wedges run uninterruptedly 
in a longitudinal direction along each joint or inter- 
node of the calamite, but at each node their arrange- 
