148 



THE RADIOLAR1A 



Faroe Channel, Shetland s ; Aulographis zctesios, Borg. ; A. furcellata, 

 Wolf., Faroe Channel ; Au. tetrancistra, H., Norway ; Aulodendron boreale, 

 Wolf., Faroe Channel. 



ORDER 2. Phaeosphaeria. 



Skeleton composed of an extracapsular shell or of two concentric 

 shells separated by the extracapsulum. Outer shell usually spherical. 



FAMILY 1. SAGOSPHAERIDAE. Outer shell a lattice- work with 

 triangular or areolar meshes. Selected forms : Sagena ternaria, H. ; 

 Sagosphaera trigonilla, H., cosmopolitan ; Sagenoarium sp., Jorg, Norway. 



FAMILY 2. AULOSPHAERIDAE. An outer lattice-shell alone present, 

 the hollow bars of which contain septa. Selected forms : Aulosphaera 

 flexuosa, H., Faroe Channel ; Auloscena verticillatus, H., Norway; Aulotractus 

 fusulus, H., Faroe Channel, Hebrides. 



FAMILY 3. CANNOSPHAERIDAE. Inner and outer lattice- shells present, 

 interconnected by radii. Cannosphaera antarctica, H., bipolar form. 



FAMILY 4. POROSPATHIDAE. Inner shell alone present, composed of 



two finely grained membranes ; elliptical 



,EXO. or ovoid. Mouth at the end of a curved 



--Pa. 



process. 



ORDER 3. Phaeogromia. 



A single simple shell present, variable 

 'Cc. in shape, but always provided with a 

 projecting peristome. 



FAMILY 1. CHALLENGERIDAE. Shell 

 monaxonic, composed of two layers which 

 exhibit an extremely fine diatomaceous 

 graining. Peristome toothed. Selected 

 forms : Lithogromia silicea, H., Faroe 

 Channel ; Protocystis tritonis, H., Faroe 

 Channel, Shetlands, North Sea; Pr. 

 tridens, H., Norway and Sweden ; Pr. 

 harstoni, Murray, Norway ; Pr. xiphodon, 

 H., Faroe Channel ; Ch alien geron trioden, 

 balfouri, golfense, johannix, armatum (Fig. 

 27) ; Cadium melo, Clev. ; Pharyngella 

 gastrula, H. ; Entocannula hirsutq, H. ; 

 Faroe Channel. 



FAMILY 2. MEDUSETTIDAE. Primary 

 __ shell alveolar. Peristome with articulated 



surrounded'by processes, and its aborai f eet ^ secondary shell may be developed 



surface bears a crest (Exo). The central . , J J 



capsule possesses two astropyies (As), in relation to the phaeodium. 

 b^VnThaeSeC $> "STiJ^ A. Small forms (averaging 0-1 mm 

 (From a living specimen, after Borgert.) in diain.), with primary shell and few 



radial spines. Phaeodium in primary 



shell. Euphysetta nathorsti', Clev., North Sea, Scotland ; Medusettc 

 tiara, H., Faroe Channel. 



B. Small forms (0'8-'3 mm.), with hooded primary shell provided 



Fia. 27. 



