38 PROTOZOA—RHIZOPODA CLASS I 
Haeckel divides the Radiolaria into four sub-orders, as follows :— 
A. Acantharia.—Capsule-membrane uniformly perforated; skeleton com- 
posed of acanthinic spicules. Unknown in fossil state. 
B. Spumellaria.—Capsule-membrane single, pores distributed all over ; 
skeleton silicious, spherical, or discoidal, sometimes wanting (Fig. 48). 
C. Nasselaria.—Capsule-membrane single, perforated only about the oral 
pole ; skeleton silicious, helmet- or cap-shaped, conformation of poles dissimilar 
(Figs. 49, 50). 
D. Phaeodaria.—Capsule-membrane double, perforated by one main opening 
prolonged into a tubulus, and by a few smaller accessory openings. A dark 



Fic. 46. 
Silurian and Devonian Radiolarians: A, Cenosphaera macropora, Riist. Ordovician ; Cabriéres, Languedoc. 
B, Staurolonche micropora, Riist. Ordovician; Cabriéres. C, Caryosphaera Groddecki, Rist. Upper Devonian ; 
Schiibenholz, near Elbingerode, Harz Mountains. D, Lithocampe Tschernytschewii, Riist. Devonian; Ural. 
Magnified 100—120 diameters (after Riist). 
pigment body (phacodium) constantly present in extra-capsular sarcode. Skeleton 
commonly consisting of hollow silicious spicules disposed in flask-shaped or 
variously shaped frameworks. Unknown in fossil state. 
Radiolarians are exclusively marine organisms, and are found at all bathy- 
metric zones. They occur in vast numbers, especially in tropical seas, 

Fia. 47. 
A Carboniferous, Jurassic, and Cretaceous Radiolarians: A, Stawracontium inaequale, Riist. Carboniferous ; 
Sicily. L, Trochodiscus Nicholsoni, Riist. Carboniferous; Harz. C, Xiphodictya acuta, Riist. In coprolite 
from Lias ; Ilsede, Hanover. D, Hymeniastrum rotundum, Riist. In coprolite from Cretaceous ; Zilli,{Saxony. 
swimming on the surface, as well as at medium and even abysmal depths ; 
particularly between 2000—4000 fathoms in depth, extensive deposits of 
“ Radiolarian mud” have been found, the composition of which is largely silica 
with a small percentage of carbonate of lime. 
The diversity of form exhibited by Radiolarians is most astonishing, and 
the identification of their microscopic silicious skeletons is impossible without 
