78 
McLean . — On the Fossil Genus Sporocarpon. 
and equal to more than half the diameter of the whole organism. A slight 
constriction develops just above the basal pore. In the oldest stages all 
the apical moiety of the spines may get knocked off, leaving only the 
disorganized basal portions. This can hardly have taken place during life, 
for the protoplasm would have been thus exposed through the broken ends. 
The breaking off of the spines in this way, found similarly in 5 . elegans , 
is evidence of fragility, which we might well predict from the general 
delicacy of the walls throughout development, but which is in striking 
contrast to the great flexibility that is evident in the spines of Traquairia . 
A somewhat rare species. I have not seen more than half a dozen 
specimens, and none of these contained any reproductive cells or capsule. 
In size it is somewhat smaller than 6'. comp actum, even in its greater diameter, 
though the spines are much longer, both relatively and absolutely. 
The following are the principal elements : 
Length of vesicles, {circa) 67 /z. 
Breadth, 16/x. 
Length of mature spine, 1 55 /a. 
Breadth at swelling, (circa) 25 /u. 
Proximal pore, 2*5-4 /a. 
Williamson, ‘Phil. Trans.’, 
Diameter over all : 
Greatest, 286 \x. 
Least, 276 fx. 
Diameter of interior : 
Greatest, 1 49 ju. 
Least, 133 \i. 
(iii) 5 . Oidospora : mihi. Oidospora anomala, 
pp- 169-357. 1878. 
This species is anomalously small, but otherwise seems to fall suitably 
into line with the two preceding organisms, in the present class. It consists 
of a spherical central portion, enclosed within an envelope of somewhat 
rounded vesicles, as closely set as their shape permits, and flattened at their 
bases, where they are attached to the wall of the sphere. No perforations 
have been observed, either to the exterior or to the interior, and the walls 
are all perfectly thin and smooth. The vesicles of the envelope are about 
equal to the diameter of the sphere in length. Although somewhat like 
N. compactuni no intermediates between the two are known. The present 
species is probably therefore a substantive one. 
Only two preparations have come under my notice, so that it is 
probably the most infrequent of the known forms. One of these is in the 
Williamson Collection at the British Museum (section numbered in catalogue 
1552), containing large numbers, from among which Fig. 102 in Williamson’s 
ninth memoir was taken. The other slide, containing only a pair, is in the 
University College London, Collection. Like most of the others, this species 
appears to have been gregarious, judging from the large numbers on one 
slide, but there is no definite sign of union into colonies. On slide W. 1552 
there are a few individuals with markedly enlarged and elongated vesicles, 
suggesting, though not conclusively, elongation into spinous processes. 
No interior capsule or spores have been found. 
