40 i^iö Royal Society, London. 



100 sections, transverse and longitudinal, having been exarnined 

 from one specimen alone. 



The principal specimens are four in number, in addition to 

 wbich other fragments have been included in the investigation. 

 The species, wbich is very distinct from any form previously de- 

 scribed, will be known as Medullnsa anglica; a diagnosis is given 

 below. 



The raost complete specimen et' the stem has a mean diameter 

 of rather more thau 7 cm., including the adhereut leaf-bases. The 

 others do not appear to have been very different in dimensions. 



The large h af-bases, to judge from the most perfect specimens, 

 alsmost completely clothed the surface of the stem. They were de- 

 current, and conöuent with the stem for a vertical distance of 13 cm. 

 or more, the diameter of the petiole, where is became free from 

 the stem, being about 3 or 4 cm. The arrangement of the leaves 

 was a Spiral one, and in the only case where the phyllotaxis could 

 be determined, the divergence proved to be 2/5. 



In two of the specimens the external characters of the fossil are 

 well shown. The outer surface of the long leaf-base is marked 

 by a conspicuous longitudinal striation, the ribs (whicli would not 

 have been so prominent during life) representing the fibrous Strands 

 of the hypodermal tissue. The habit of the stem, clothed with the 

 long, almost vertical, overlapping leaf-bases, may have been not 

 unlike that of some of the tree-ferns, such as Alsoijhila procera. 



The vascular System of the stem consists of three ; or locally 

 four) steles, anastomosing and dividing at long intervals. Each stele 

 lias an elongated, somewhat irregulär, sectional form, and is composed 

 of a central mass of priraary wood, surrounded by a zone of se- 

 condary wood and phloem. The pi'imary wood, which is very well 

 preserved, is raade up of tracheides and conjunctive parenchyma, 

 with the Spiral Clements (protoxylem) scattered near its outer margin. 

 The secondary wood consists of radial series of tracheides and rae- 

 dullary rays ; the secondary tracheides bear multiseriate bordered 

 ])its on their radial walls; most of the primary tracheides are pitted 

 in the sarae way, but on all sides alike. In the neigbourhood of 

 tiie protoxylem-groups the tracheides of the primary wood are spiral 

 or scalariform. The phloem is made up of elongated Clements, 

 ])resumably the sieve-tubes, forming a network, the meshes of which 

 are occupied by the phloem-rays. 



Each Stele of Medullosa anglica shows the dosest agreement 

 in structure with the Single stele of a Heterangium^ so that the stem 

 of this Medullosa might well be conciseley described as a polystelic 

 lleterangium. 



Tlie course of the leaf-trace bundles was followed very completely 

 in consecutive series of transverse, and in longitudinal, sections. 

 The leaf-traces leave the steles precisely in the same manner as in 

 Jhterangium. On becoming free the trace is a large concentric 

 bündle, surrounded by its own zone of secondary wood and hast. 

 As it passes obliquely upwards through te cortex, the trace loses 

 its secondary tissues, and undergoes repeated division into a number 



