82 McLean. — On the Fossil Genus Sporocarpon. 
show a complementary jutting of the inner surface of the sphere wall. The 
sporoids and periplasm are exactly as in other species. 
Williamson described and named as species of Sporocarpon (S. ano- 
malum and .S. ornatum ) 1 two objects with just such a parenchymatous 
investment as this, which have since been shown to be the transverse 
sections of small Pteridospermic seeds. 2 Indeed they show many features 
which might have aroused suspicion of their nature. One might easily 
dismiss the present species as an impostor and thus be rid of a peculiar 
difficulty, were it not for the very clear evidence of the capsule and its spore 
contents, which are perfectly in accord with the same structures throughout 
the group. 
Similarly, S. asteroides agrees with other species in secondary points ; in 
the matter of size, for example (though this is rather variable, within limits), 
and in its gregarious habit, so that I cannot but regard it as an established 
member of the genus, albeit not easy to bring into line with the remainder. 
The diameter of the sphere is rather more variable than is usual, 
although all species exhibit some plasticity in this respect, strengthening 
the view that the interior cavity is an integral living part of the organism. 
Growth is straightforward, the original form being without projecting lobes, 
which develop secondarily, but early, upon a narrow, spherical envelope 
of cells. 
Dimensions : 
Width of sphere, 180-330^. 
Length of lobes, 1 20-140 y. 
Width of lobes at base, 90—120 /x. 
Average thickness of envelope between lobes, 25 /x. 
Size of individual cells, 8-16 \x. 
§§§§§ Perichoderma. 
S. pachyderma. Williamson, 6 Phil. Trans.’, pp. 171-510, 1880. 
An interesting and frequent species. The envelope is composed of 
large interlacing tubules, anastomosing closely with one another in all 
directions. Neither beginning nor end is traceable for any given tubule : 
all are fused into a closed system round the stout wall of the sphere. At 
the external surface certain tubes form extruding apertures which there is 
reason to believe may have formed the bases of radial processes, usually 
lost or crushed, but as they stand they merely provide communication 
between the lumen of the tubular network and the outside. Usually all 
the ramifications are approximately of equal diameter, but there is a second 
type distinguishable where certain larger and darker walled tubes form 
1 Phil. Trans., 1880 and 1883. 
2 Oliver, Ann. Bot., xxiii. 74, 1909. The statement that S. anomalum is a mere slip for 
.S’, ornatum is not correct, for the original specimen , W. 1326, is so labelled by Williamson. Nor 
are the two altogether identical, though the differences may be due to their respective states of 
preservation. 
