EECENT RESEARCHES ON THE RADIOLARTA. 



179 



Subsection 2. ETHMOspniERiDA. 



One, or two or three circumferential shells united by radii ; if 

 one, then formed of a delicate network with irregular meshes. 

 Grenera : Cyrtidosphcsra^ EthmosphcBra, Arachnosplicera. 



Subsection 3. AcANTnonESMiDA. 

 Shell consisting of a few irregularly united bands. G-enera : 

 Lithocircus, Zygosteplianus, Acanthodesmia, Plagiacantha, Frisma- 

 tium, Bictyocha. 



Section VI. COLLOZOA. 

 Simple or compound Eadiolaria ; if single, then with the ske- 

 leton in the form of circumferential detached spicula only. No 

 nuclear vesicle. 



Subsection 1. Polycollida. 

 Compound Eadiolarians. 



Subdivision i. Sphcerozoida. 



Skeleton absent, or consisting only of scattered spicula. Genera : 

 Collozoum, SpJicerozoum, Bliaplndozoum. 



Subdivision ii. Collosphcerida. 



Skeleton a spheroidal perforated shell. G-enera: Siphonosph(era, 

 CoUosphara. 



Section YII. YESICULATA. 

 Eadiolaria with a nuclear vesicle. 



Subsection 1. Collida. 



Skeleton wanting, or consisting only of scattered circumferen- 

 tial spicula. G-enera : Thalassicolla, Thalassolampe, Aulacmitha, 

 Fhysematium. 



Subsection 2. Sph^roidea. 

 Vesiculata with one or more concentric extracapsular shells 

 bound together by radii. Genera ; Heliosphcdra, Diplosphwra ? 



Subsection 3. Atilosph^rida. 



Vesiculata with a complex circumferential skeleton of hollow 

 bars. Genus Aulosphcera. 



Subsection 4. Beaohiata. 



Vesiculata with the extracapsular sarcode prolonged into one 

 or more arm-like processes. Genus Myxohrachia. 



