1906-7.] Internal Structure of Sigillaria mamillaris , etc. 203 
XXI.— Preliminary Note on the Internal Structure of Sigillaria 
mamillaris, Brongniart, and Sigillaria scutellata, Brongniart. 
By R. Kids ton, F.R.S. L. & E., F.G.S., Foreign Mem. Kaiserl. 
Mineral. Gesell. zu St Petersburg. 
(MS. received July 2, 1907. Read July 15, 1907.) 
A FEW months ago I received from Mr G. H. Knott three specimens of 
Sigillaria from the Halifax Hard Bed of Yorkshire having the structure 
of their steles and outer cortex well preserved. 
In two of these specimens the coal-ball containing the fossils so split 
that the outer surface of the cortex became exposed, exhibiting the leaf 
scars in a fine state of preservation, from which a specific identification of 
the two plants was easily made. 
One of these was Sigillaria mamillaris, Brongt., and the other Sigillaria 
scutellata, Brongt. The third specimen from the structure of the stele is 
seen also to belong to Sigillaria mamillaris, Brongt. 
Both these species belong to the Rhytidolepis, or ribbed section of the 
genus Sigillaria, of which group the internal structure was hitherto only 
known of Sigillaria elongata, Brongt.,* and Sigillaria elegans, Brongt. f 
Sigillaria mamillaris, Brongniart. 
The stele of the specimen showing the outer cortex from which the 
specific identification was made has suffered from lateral pressure. The 
continuous xylem ring is fractured and the separated portions somewhat 
displaced. In certain parts of the stele an original tare in the specimen 
has separated the centripetal from the centrifugal xylem, but in other 
portions they are still in organic union. The xylem ring is 4 mm. wide, of 
which the primary xylem occupies about 1‘50 mm. (fig. 1). 
The primary xylem consists of a continuous band whose outer margin 
is distinctly crenulated, the crenulations having slightly flattened apices. 
These apices consist of the small protoxylem elements which are arranged 
at their widest part in three or four rows, the smallest tracheids being outer- 
* Bertrand, Annals of Botany, vol. xiii., 1899, p. 607. 
t Kidston, Trans. Roy. Soc. Edin., vol. xli., p. 533, 1905, Pis. i.-iii. 
