290 A. OC. Seward—Calamites undulatus. 
regards the flexuous character of the furrows to have been imparted 
by pressure, any Calamite being liable to a bending of its furrows 
from the same cause. 
The specimen now described and figured (Plate IX. Fig. 1. A. 
B.) is a pyritous sandstone cast of the medullary cavity of a Calamite, 
showing two internodes and one node. I found it in a piece of rock 
which had been brought to the surface in sinking a shaft at a colliery 
near Wigan. 
Figures 1 A, and 1 B. are opposite sides of the same specimen. In 
Fig. 1A, the ribs are perfectly straight and close together. No “‘infra- 
nodal canals” are visible on either side of the specimen. At the left- 
hand upper corner of Fig. 1 A, the ribs become wide and irregular : in 
Fig. 1 B, these characters are still further developed, the ribs and 
furrows now having a decidedly flexuous appearance. In Fig. 1 A, 
there are about eight ribs in a space of one cm., in Fig. 1 B, three 
occupy the same space. The length of the specimen is different on 
the two sides, the side with the straight ribs and furrows being 10cm. 
long, and that with the flexuous ribs 9cm. The ribs and furrows 
alternate at the node. 
On many of the ribs there is a faint median line visible, which is 
in some parts rendered more conspicuous by the presence of carbon- 
aceous matter. This difference in the breadth of the ribs on the 
two halves of the specimen is probably due to the original arrange- 
ment of the vascular wedges and medullary rays in the living 
Calamite. Prof. Williamson’ has figured a transverse section of a 
Calamite in which the distance between the woody wedges varies in 
the two halves of the stem, the medullary rays being narrow in the 
one half and wide in the other half of the section. In Prof. 
Williamson’s collection of microscopic slides, which I have had an 
opportunity of examining through his kindness, I have met with 
other specimens showing the same inequality in the size of the 
medullary rays on the opposite sides of the section. 
In the Woodwardian Museum there is a flattened cast of the 
medullary cavity of a Calamite which shows the same characters 
still more clearly (Pl. IX. Fig. 2 A, B). The specimen is 18 cm. 
long and 6:5 cm. broad. On the side shown in Fig. 2 A, the ribs are 
straight and close together; on the side shown in Fig. 2 B, they are 
wide and flexuous. ‘“Infranodal canals” are clearly shown on the 
side with wide and wavy ribs, but less distinctly on the opposite side. 
The following measurements show that the internodes on the side 
with the wide and flexuous ribs are shorter than those with the 
narrow and straight ribs :— 
(Plate IX.) 
Fig. 2 A. Fig. 2 B. 
(Number of ribs per cm. 35.) (Number of ribs per cm. 17.) 
Length of internode i. 3-9 cm. Length of internode i. 3°5 cm. 
* 0 li. 4 cm. a Be ii. 3:7 cm. 
ae 3 iu. 4°2 cm. At . i, 3:0 cm. 
A ms iv. 3°9 cm. iN a lv. 3:7 cm. 
1 Phil. Trans. Royal Soc. 1883, On the Organization of Fossil Plants of the 
Coal-measures, pt. xil. pl. 33, fig. 19. 
