OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
521 
The most indisputable feature which they present is that they are all hollow spheres, 
most of which are furnished with varying forms of peripheral appendages. The true 
sphere-wall is always darker than either the investing matrix or the contents of the 
spherical cavities when examined by transmitted, and lighter when seen by reflected, 
light. In these respects the conditions are identical with those presented by the shells 
of Foraminifera seen in the same matrix. The differences seen in various parts of each 
object are of material value in enabling us to distinguish between primitive organic 
elements and secondary infiltrated ones. The former appear to be always opaque, and 
to exhibit structural organic features. The latter are always translucent and crystalline. 
Differences are further observable according to whether a very thin section is taken 
out of the centre of a sphere, or whether a sphere is merely cut into two equal or 
unequal halves. 
The discrimination of species, when we only know the objects through sections of 
them, is always difficult and sometimes impossible. At the same time it is often 
desirable that we should have provisional names whereby to recognise certain typical 
forms. Hence I venture to follow the plan adopted in the case of the Foraminifera , 
in which latter the purport of the names, generic as well as specific, is understood to 
have no reference to real genetic distinctions. I propose for the objects under considera¬ 
tion the generic name of Calcisphcera, as not involving any premature hypothesis 
respecting their nature. 
Fig. 70 represents the inner portion of a hemisphere of C. Ice vis, viewed as an opaque 
object. I select this for our first consideration, because it exhibits these organisms in 
their simplest form. Its maximum diameter is about ’006, whilst the thickness of the 
sphere-wall is about ’00058. I can detect no trace of structure in the sphere-wall, 
neither has it any peripheral appendages. It is simply a smooth sphere—with a thick 
sphere-wall and an equally smooth internal spherical cavity—the latter portion being 
occupied by a crystalline calcic carbonate, which has obviously reached the cavity as a 
solution that filtered through the permeable sphere-wall. 
Fig. 79, Calcisphcera cancellata. —This is rather a rare form. The drawing represents 
a thin equatorial section viewed by transmitted light. The central sphere cavity is 
filled with infiltrated crystalline calcic carbonate. The sphere-wall is now not only 
double, but the inner and outer layers enclose between them numerous small cubical 
compartments separated by radiating partitions. The compartments are filled, like 
the central sphere-cavity, with infiltrated translucent calcic carbonate. This object is 
of the same size as fig. 70. 
Fig. 67, Calcisphcera fimbriala, is also of the same maximum size as fig. 70, though, 
like that object, we find it of very variable dimensions, the smallest specimen being 
not more than an eighth part of the diameter of the larger ones. The central sphere- 
cavity as seen by transmitted light is filled with crystalline infiltrated calcic carbonate. 
This is surrounded by a dark sphere-wall, which is obviously not homogeneous, but 
has rather the appearance of being composed of radiating fibres. I suspect that this 
