250 PROF. W. €. WILLIAMSON ON A NEW FORM 



by the presence in its interior of some of the ubiquitous 

 rootlets of Stigmaria in an uncompressed condition. Ex- 

 tending from this medullary cavity to the periphery of the 

 base of the strobilus is an almost unbroken disk of cel- 

 lular membrane, the surface of which, under a low mag- 

 niiier, exhibited myriads of very fine radiating striae, run- 

 ning from the centre to the circumference. This hori- 

 zontal disk was not extended in one plane, but variously 

 inflected, presenting, when seen from below, two inner 

 circles, each of which was slightly convex, surrounded by 

 a larger concave one. Immediately surrounding the me- 

 dulla is an unbroken ring about ^-J-^ of an inch in breadth, 

 perfectly flat, save at its inner border, where it is convex ; 

 but I doubt if this convexity existed in the living strobilus. 

 From the outer margin of this ring the disk is extended 

 in the same plane for rather more than the ^^ of an inch. 

 In this latter portion we have a circle of symmetrically 

 arranged pyriform figures, also filled with crystalline carbo- 

 nate of lime. These figures indicate open spaces, dividing 

 the membranous disk into ten principal inner peduncles 

 and twenty secondary outer ones. A little beyond the outer- 

 most boundary of these spaces, the disk has bent downwards, 

 forming on the inferior surface of the segment a convex 

 ring, enclosing the parts just described, after which the 

 disk reverses its direction, forming a concave space that 

 extends to the acute inferior peripheral margin (fig. 2 b) 

 of the internode. At this point the disk subdivides into a 

 multitude of minute ovato-lanceolate bracts, which bend 

 abruptly upwards, and which constitute, as already de- 

 scribed, the outermost investment of the strobilus. 



Fig. 3 represents a transverse section of a portion of the 

 Strobilus, made in the plane of the flat disk surrounding 

 the pith of fig. 2, being, in fact, a section of part of the 

 central axis of the strobilus, where it passes through a nodal 

 bractigerous verticil : c c represent two of the ten primary 



