42 Dr. G. J. Hinde on Radiolaria from the 
of the Radiolaria, which appear as minute, clear, circular 
specks ; in thin sections of the unstained rock under the 
microscope they look like larger and smaller shadowy circles 
tilled with a somewhat lighter material than the surrounding 
matrix ; but in this condition no structure has been pre- 
served. In sections of the red or jaspery chert the outlines 
of the Radiolaria are more clearly defined ; the inner tests are 
occasionally shown as small red globes in the centres of larger, 
nearly transparent spheres, and not unfrequently the radiating 
spines are also indicated. In the red jaspery chert the enor- 
mous number of these organisms in the rock can be clearly 
seen, for the entire area of the section is occupied by their 
small circular outlines, which range from *01 to *25 millim. 
in diameter. 
In the unstained and reddish chert just referred to the 
Radiolaria are only represented by casts, their tests having 
been dissolved or otherwise rendered undistinguishable ; but 
where the chert has been stained by the darker substance 
mentioned above, which may be either due to carbon or iron, 
the tests themselves have been preserved in this material, 
which has replaced the original silica. In this condition the 
delicate lattice-like structure of many of them is now repre- 
sented by a more or less dark meshwork, which, though as 
regards clearness of outline cannot be compared with the tests 
of recent or Tertiary fossil Radiolaria, is yet sufficient to show 
that the structure of these Palaeozoic forms is essentially of 
the same character as that of their modern descendants. In 
these stained portions, which, as already noticed, occur as 
irregular patches in the generally transparent rock, fairly 
perfect specimens of Radiolaria showing one or more concen- 
tric spheres, and spines projecting from their surfaces, are 
intermingled with fragments of the meshwork, and entire and 
broken spines of other individuals, much in the same way as 
the entire forms and the fragmentary debris of these organisms 
occur in the unconsolidated Radiolarian earth from Barbados. 
It is, however, often very difficult to ascertain with pre- 
cision in the sections those particular features which form the 
basis of most of the family and generic characters in Haeckel’s 
classification of these organisms. The tests are usually so 
filled with the dark staining material that they are either 
entirely opaque or present a blurred appearance. In these 
cases it is impracticable to determine definitely whether the 
structure was originally u lattice-like or of an irregularly 
reticulate or u spongy ” character, or whether an inner medul- 
lary test is present or not. The specimens available for study 
are limited to those shown in the sections of the chert, and 
