nmzopoBA. 



11 



2. Flagelliteea. — This gi-oup receives its name from the flagellum which charac- 

 terizes the species belonging to it. 



3. ENTOsPHiEEiDA. — In this group the organisms are provided with an intrarcapsu- 

 lar, spheroidal shell, not traversed by radii, in this respect differing from the Discida. 

 They have no nuclear vesicle. The typical genus is Haliomma, of which there are 

 many forms. Haliomma polyacanthum is represented in Fig. 6. 



4. AcANTHOMETEiDA. — The members of this division are characterized particularly 

 by a well-developed radial skeleton, the radii meeting in the centre of the capsule. There 

 is no enveloping shell, but lateral processes sometimes project from the spines, as in the 

 beautiful Xiphacantha found by the " Challenger " expedition, represented in Fig. 7. 



Fig. 7. — Xiplmcantha, magnified 100 times. 



5. PoLTCYSTiSTA. — The Polycystina are by far the most numerous in all fossil 

 deposits of Radiolaria. They are very simple forms with skeleton external, more or 

 less compact or continuous, without a nuclear vesicle. The shell may be a simple 

 sphere, or two or three concentric spheres connected by radii, or with external radial 

 outgrowths extending to a length of several times the diameter of the shell. The 

 most numerous forms, however, belong to the genera Podocyrtis and Eucyrtidium, 

 the former represented in Fig. 8. The beautiful Eucecryphialus (Fig. 5) also belongs 

 to this group. In these forms the shell opens at one end, and growth being mainly 

 in one direction said to be unipolar. 



6. CoLLOZOA. — To this group belong a number of soft, gelatinous forms which are 

 frequently aggregated in colonies, and are therefore designated as compound Radio- 

 laria. The animals may be either single or in families. When single the skeleton con- 

 sists of circumferential spicules, isolated from each other. When compound, there 



