88 McLean . — ( 9/2 the Fossil Genus Sporocarpon . 
The genus Calcisphaera , too, may have originated fin this period, although 
it makes its appearance earlier, in the Carboniferous Limestone. Hill and 
Jukes-Browne ( 9 ) have shown how unstable chemically is the Radio- 
larian skeleton during fossilization, and Calcisphaera may likewise have 
suffered chemical replacement of either a siliceous, strontium sulphate, or 
organic test by calcite. Apart from its chemical nature there is little to 
separate it from true Radiolaria, and it affords several morphological links 
between them and the Traquairidae. Taking into account its earlier 
appearance and its intermediate distribution, in the moderately deep water 
limestone deposits, it may well be a connecting group. 
Summary. 
1. The present article is an attempt to give in full detail the facts, in 
so far as they have been determined, of the structure of the genus 
Sporocarpon , Williamson, one of the group of Traquairidae, previously 
established (1). 
2. The genus is shown to cover a multiplicity of divergent types, 
represented only by single species, which it is impossible to regard as 
generically related in the present-day sense. The old generic name is 
retained for convenience, but five subgenera are proposed. 
3. A revised monographic description of the seven species is given. 
The organism called by Williamson Oidospora anomala is added to the 
present genus under the name of Sporocarpon Oidospora. 
4. Taking 5 . compaction as the simplest and least specialized type, it 
is shown that it is possible to derive the structure of the other species from 
it by divergent changes, while Traquairia may also be derived from 
a Sporocarpon type, probably in the neighbourhood of 5 . cellidosum. This 
emphasizes the homogeneity of the group. 
5. The relationships of structure between Sporocarpon and recent 
Protozoa are examined in detail and the conclusion pointed that the nearest 
living analogues of Traquairidae are the Peripylarian Radiolaria. At the 
same time the material of the skeleton and the appearance of the spores 
suggest that, like the Radiolaria, they may ultimately have sprung from 
flagellate ancestors of a Peridinian type. 
6. Evidence is adduced for the widespread existence of Radiolarian 
organisms at the base of the Carboniferous period in abyssal waters ; while 
in the shallower water limestone deposits of the Lower Carboniferous, the 
intermediate organisms called Calcisphaera are enormously prevalent. 
The bearing of this upon the phyletic origin of Sporocarpon , afterwards 
typically developed in the non-saline waters of the Coal Measures, is pointed 
out and suggested as a probable trace of their evolution. 
7. These organisms are specially characteristic of sections taken from 
coal-seam nodules (coal-balls) of the Lower Coal Measures, and in particular 
