Medullas a from the Lower Coal Measures . 263 
VIII. Diagnosis. 
Medullosa centro fills , sp. nov. 
Stem small 5x1-5 cm., including the leaf -bases, completely clothed 
by spirally arranged, decurrent leaf-bases, four in number. 
Vascular system of the stem composed of a ring of three or four steles, 
irregular in transverse section, enclosing a central star-ring. Interior of each 
stele occupied by primary wood. 1 
Secondary wood developed round each of the steles. Tracheides with 
bordered pits on the radial walls. 
Leaf-traces leave the stele without any secondary wood ; branching 
almost immediately into collateral strands. 
Leaf-bases with the structure of Myeloxylon Landriotii , Ren. 
Secretory canals abundant in the leaf-bases and around the steles of 
the stem. 
Locality. Shore Littleborough Colliery, Lancashire. 
Horizon. Lower Coal Measures. 
The characters in which the species differs from both M. anglica and 
M. pusilla are italicized. It also differs from M. anglica in the absence of 
secondary tissues in the leaf-trace, and from M. pusilla in the structure of 
the hypoderma. 
IX. Summary. 
1. Structure (Sections ii-vi, pp. 252-261). The specimen consisted of 
a stem entirely clothed by portions of four spirally arranged, adherent 
leaf-bases. 
(a) Stem. 
The vascular system consists of an outer series of three or four uniform 
steles, surrounding a single, central star-ring. The structure of the steles 
and of the star-ring is essentially similar to that of a single stele of Medullosa 
anglica. The steles are surrounded by a well-preserved zone of tissue, 
morphologically periderm, but functionally secondary cortex. 
Leaf-trace strands are given off from the peripheral region of the outer 
stelar ring. They are not accompanied in their exit by secondary tissue, 
and immediately begin to divide up into collateral bundles. 
(b) Leaf-base. 
The ground tissue consists of thin-walled parenchyma, in which 
numerous mucilage sacs occur. 
Many leaf-trace strands occur in the ground tissue ; they are collateral, 
with exarch protoxylem abutting on a space representing the phloem. 
A single layer of fibres surrounds the xylem, and most of the strands are 
enclosed in a sheath, in the cells of which cambial divisions occur. 
1 Protoxylem probably exarch. 
