THE RADIOLARIA 147 



fined to the two polar apertures. The genus Diploconus is known from 

 the Mediterranean. 



SUB-CLASS III. MONOPYLARIA (Nassellaria). 



Radiolaria with monaxonic central capsule that bears at one pole a 

 porous plate forming the base of an inwardly directed cone. 



SOB-LEGION 1. Plectellaria. 



Without a complete lattice-shell. 



ORDER 1. PLECTOIDEA. Skeleton a basal tripod (Fig. 5). Selected 

 forms : Plagiacantha arachnoides, Clap., W. coast of Norway, North Sea ; 

 Plagiocarpa procyrtella, EL, North Atlantic, Iceland ; Hexaplagia arctica, 

 H., Greenland ; Polyplagia novenaria, H., Faroe Channel, North Atlantic ; 

 Plectophora arachnoides, H., and PI. novena, H., North Atlantic and Faroe 

 Channel, North Sea. 



ORDER 2. STEPHOIDEA. Skeleton a sagittal ring, and usually no 

 tripod. Selected forms : Lithocircus annularis, Mull. ; Cortiniscus 

 iypicus, H. ; Eucoronis nephrospyris, H. ; all cosmopolitan. 



SUB-LEGION 2. Cyrtellaria. 



Skeleton a complete lattice-shell (cephalis). 



ORDER 1. SPYROIDEA. Cephalis bilocular with cephalic construction. 

 Almost exclusively southern forms. 



ORDER 2. BOTRYOIDEA. Cephalis multilocular. Selected forms : 

 Sotryocampe inflata, Ehr., cosmopolitan ; Phormobotrys hexaihalomia, H., 

 Mediterranean. 



ORDER 3. CYRTOIDEA. Cephalis single, without constrictions or lobes. 

 Selected forms : Tridictyopus elegans, Hert., Mediterranean ; Cornutella 

 lathrata, Ehr., cosmopolitan ; Cyrtocalpis obliqvM, H., cosmopolitan ; 

 Lithomelissa thoracites, H., cosmopolitan ; L. setosa, H., Norway ; Eucecry- 

 phalus gegenbauri, H., cosmopolitan ; Carpocanium diadema, H., cosmo- 

 politan ; Dictyocephalus ocellatus, H., Faroe Channel ; Dictyophimus clevei, 

 Jorg., Norway ; Theoconus ariadnes, H., cosmopolitan ; Cladoscenium 

 tricolpium, Norway ; Clathrocyclas craspedota, Norway. 



SUB-CLASS IV. TRIPYLARIA (Phaeodaria). 



Radiolaria in which the central capsule is double and usually 

 possesses a chief aperture (astropyle) and two accessory apertures (para- 

 pyles). A dense resistant pigment (phaeodium), probably of excretory 

 nature, accumulates in the extracapsulum. The skeleton is siliceous and 

 .often made up of hollow tubes. 



ORDER 1. Phaeocystina. 



The skeleton consists of isolated spicules. 



FAMILY 1. AULACANTHIDAE. Skeleton of tangential needles and radial 

 ; hollow rods. Selected forms : Aulacantha scolymantha, H., Hebrides, 



