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 

 fepines 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 tlie 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 HEeckel'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 "lattice-like'^ or of an irregularly 

 reticulate or " 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 



