178 PEOF. ST. GEOEGE MIVABT ON 



Subsection 2. Diploconida. 

 Skeleton a double one, with radii also. G-enus Dijjloconus. 



Subsection 3. Catapheacta. 



AcantJiometrida with outgrowths at right angles from their 

 radii forming a circumferential structure. Genera : Dorataspis, 

 Haliommatidium . 



Section V. POLTCYSTINA. 



Simple, ectolithic Eadiolarians with more or less compact ske- 

 letons, often with unipolar growth. No nuclear vesicle. 



Subsection 1. Gyetida. 



Shell an external, more or less continuous, but perforated case 

 variously formed, mostly with an open mouth at one pole ; shell 

 growing from one pole. No radial skeleton except external spines. 



Subdivision i. Monocyrtida. 



Shell single, without divisions. Genera : LitharacJinium, Cornu- 

 tella, Gyrtocalpis, PylosjphcBra, Spirillina, Haliphormis, Halica- 

 lyptra, Carjpocanium. 



Subdivision ii. Zygocyrtida. 



Shell divided by a vertical constriction. Genera : Dictyospyris, 

 Ceratosiyyris, Cladospyris, Petalospyris. 



Subdivision iii. Dicyrtida. 



Shell divided by a transverse constriction. Genera : Dictyocepha- 

 lus, Loplioph(sna, Clathrocanium, Lamprodiscus, Litliopera, Litho- 

 melissa, Araclmocorys, DictyopMmus, Eucecryphalus, Antliocyrtis , 

 Lyclmocanium. 



Subdivision iv. SticJiocyrtida. 



Shell divided by two or more transverse constrictions. Genera : 

 Eucyrtidium, Litliocampe, Thyrsocyrtis, Litliocorytliium, Fteroca- 

 nium, Dictyoceras, Lithornitliium, HJiopalocanium, Pferocodon, Po- 

 docyrtis, Dictyopodium. 



Subdivision v. Polycyrtida. 



Shell divided by several transverse or vertical constrictions. 

 Genera : Spyridobotrys, Botryocampe, Lithohotrys, Botryocyrtis. 



