McLean. — On the Fossil Genus Sporocarpon. 8r 
Proximal pores communicating with the interior have been seen at 
the base of the radial tubuli. Central capsule and reproductive cells 
normal. 
No certain developmental phases have been observed, but a spherical 
body with an envelope of a single layer of small square cells with dark 
walls, once found, suggests a possible juvenile form. 
Dimensions : 
Total diameter, 400-420 /x. 
Diam. of sphere, 350 /x. 
Length of best-developed processes, 65-70 /x. 
Width of such processes, 20-23 /x. 
Length of short processes, 15-30 /x. 
§§§§ Sirion. 
S. asteroides. Williamson, Phil. ‘Trans.’, pp. 171-510, 1880. 
A strikingly peculiar species, in which the envelope consists of a firm 
parenchymatous tissue, or what appears to be such, though it may actually 
be paraplectenchyma, the difference being obscure even in isolated sections 
of living plants, and almost indecipherable in a fossil. The great regularity 
in size and arrangement of the cells does, however, look very like true 
parenchyma. The envelope is produced into large lobes, nearly as long as 
the organism is wide, five or six of which may appear in any section. 
Hence the specific name. 
The walls of most of the cells are quite thin, except at the outer surface 
and in particular at the tips of the rays, where there is marked induration 
and darkening. Faint markings are sometimes discernible on the walls,, 
but no cell-contents have been seen. The inner layers of the envelope are 
sometimes markedly meristematic in appearance, and this, in conjunction 
with the thickened walls and absence of divisions in the outer layers, points, 
clearly to centrifugal growth of the envelope. The outer surface is very 
seldom well preserved ; in fact, the only perfect outer surface I have seen,, 
and that one irregular, was in a young specimen with very small lobes,, 
which suggests that the outer surface was subjected to erosion during later 
life and was worn away and renewed internally like so much periderm. 
The average depth of the envelope is 5-6 cells, but a lobe when mature 
may be more than a dozen layers in depth, while in the bays between lobes 
there may be only one layer. No perforations of any sort are visible, and 
it is rather difficult, with this in mind, to envisage any but a holophytic 
method of nutrition. 
The capsule wall is peculiar, for it can be clearly seen under high 
magnifications (500 diam. et supra) to be patterned with very minute and 
closely set dots. In transverse section these dots show up as raised papillae 
on the outer surface of the capsule wall, while especially favourable examples 
H 
