176^^ 



PROF. ST. GEORGE MIVART ON 



quite irregularly disposed, but whieli generally form an external 

 perforated shell with an internal partition or spheroidal mass 

 forming a series of mutually communicating chambers, which are 

 either concentrically or spirally arranged : no flagellum ; growth 

 multipolar or centrifugal ; no nuclear vesicle. 



Subsection 1. Coccodiscida. 

 One or more concentric shells included within the internal 

 shell. Genera : Coccodiscus, Lithocyclia, Stylocyclia, Astromma, 

 Hymeniastrum. 



Subsection 2. Trematodiscida. 



Central chamber not different from the other and concentric 

 chambers. Grenera : Trematodiscus, PericJilamydium, Stylodictya, 

 Mliopalastrwn, Stejphanastrum, Ilistiastrum. 



Subsection 3. Discospirida. 



Central chamber not different from the other and spirally ar- 

 ranged chambers. Grenera : Discospira, Stylospira, Stylospongia. 



Subsection 4. Lithelida. 



Skeleton spheroidal, with the interior containing a mass of 

 spirally arranged chambers. Litlielius. 



Subsection 5. Spongida. 



Skeleton with its chambers not separated off, the radial and cir- 

 cumferential elements being irregularly scattered, except that 

 there are often radiating spines. Grenera : Spongodiscus, Spongo- 

 trocJius, Spongurus. 



Section II. FLAGELLIFERA. 



Eadiolaria with a flagellum. No nuclear vesicle. Genera: 

 Spongocyclia, Spongoastericus, EucTiitonia. 



Section III. ENTOSPH^EIDA. 



Eadiolaria with an intracapsular spheroidal shell ; not traversed 

 by radii. No nuclear vesicle. 



Subsection 1. Ommatida. 



Two or three, or more, concentric spheroidal shells. No spongy 

 skeleton. 



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