PROTOZOA : RADIOLARIA. 77 



Eocene is especially distinguished by a very widely spread and 

 easily recognised rock known as the Nunmmlitic Limestone, 

 so called from the abundance in it of a large coin-shaped Fora- 

 minifer termed the Nummulite (fig. 16). The Nummulitic 





Fig. 16. Nununulina l<evigata. Eocene. 



Limestone stretches from the west of Europe to the frontiers 

 of China ; but in some cases, in place of Nummulina proper, 

 it contains the remains of a mimetic form termed Orbitoides. 

 Upon the whole, Dr Carpenter concludes that " there is no 

 evidence of any fundamental modification or advance of the 

 foraminiferous type from the Palaeozoic period to the present 

 time." 



CHAPTER IV. 



RADIOLARIA. 



ORDER IV. RADIOLARIA. The order Radiolaria was founded 

 by Miiller to include the Polycystina, the Acanthometrina, and 

 the Thalassicollida, to which Dr Carpenter adds Actinophrys 

 and its allies, chiefly on account of the form of the pseudo- 

 podia, the latter forming a special group, to which the name 

 of Heliozoa may be given. Most of the Radiolaria are marine, 

 and the few forms which have been described as occurring in 

 fresh water, are probably best referred to the Heliozoa. 



The order Radiolaria may be defined as comprising those 

 Rhizopods which generally possess a siliceous test or siliceous 

 spicules, and are provided with pseudopodia which stand out like 

 radiating filaments, and occasionally run into one another. All of 

 the typical Radiolaria possess a central membranous or chitinous 

 capsule surrounded by an envelope of sarcode. The extra- capsular 

 sarcode generally contains a layer of yellow cells, which are com- 

 posed partly of starch. If we except Actinophrys and its allies 



