440 
SPENCER : ASTROMYELON. 
the coal-balls found in the Halifax Hard Bed Coal, and in a similar 
coal in the neighbourhood of Oldham. Very little is known res- 
pecting the external appearance, but they appear to have been for 
the most part small herbaceous plants, like Asterophyllites and 
the smaller kinds of Calamites. 
I have recently found specimens of Astromyelon both as casts 
in sandstone and as impressions on shale. In the flagstone quar- 
ries at Ringby, near Halifax, I saw the impression of a longitudi- 
nal section of the stem of Astromyelon on the face of a flags tone, 
which shewed the structure almost as perfectly as a coal ball sec- 
tion. The mural arrangement of the cells of the medulla — so famil- 
iar in examples from the coal-balls — presented the appearance of a 
wall of white bricks, while the basement layer and copings were 
represented by the narrower, and darker, and more compact lay- 
ers of the ligneous zone. The fragment was impressed on a 
filmy layer of micaceous shale and broke into smaller fragments 
when I attempted to secure it. It is evident from this fact, that 
the remains of this plant must either have been overlooked or else 
confounded with those of other fossil plants. 
The coal-ball material in the neighbourhood of Halifax has 
yielded a variety of Astromyelons, and many of them in a 
beautiful state of preservation. The transverse section of a per- 
fect stem of a typical specimen shews a central parenchymatous 
medulla, surrounded by a woody cylinder, which is composed of a 
regular series of primary wedges. These wedges are almost iden- 
tical in structure with those of Calamites, with the exception that 
the canals at the inner ends of the wedges are absent ; the 
wedges are also more obtuse than those of Calamites. The num- 
ber of wedges forming the exoginous cylinder varies from five or 
six in very young specimens, to from nine to thirteen in more 
mature ones. In Calamites the wedges are more regular and 
smaller in size, and range from eleven to sixty or more in number, 
according to the size of the plant. 
In Astromyelon the woody wedges differ considerably in size. 
