148 



THE RADIOLAR1A 



Faroe Channel, Shetlands ; Aulographis zetesios, 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 ; Sayenoarium 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 



process. 



\--Pa. 



ORDER 3. Phaeogromia. 



-Cc. 



-As. 



A single simple shell present, variable 

 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 ; Challevgeron trioden, 

 balfouri, golfense, johannis, armatum (Fig. 

 27) ; Cadium melo, Clev. ; Pharyngella 

 gastrula, H. ; Entocannula hirsuta, H. ; 

 Faroe Channel. 



FAMILY 2. MEDDSETTIDAE. Primary 

 shell alveolar. Peristome with articulated 



surroundedby processes and its aborai f eet ^ secondary shell may be developed 

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



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



two parapyles, and two nuclei. The A q 11 t (avertm-ncr 0-1 mm 



brown phaeodellae (Ph) are shown. * ln dil S ^averaging U 1 mm, 



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



radial spines. Phaeodium in primary 



shell. Euphysetta nathorsti, Clev., North Sea, Scotland ; Mediisetta 

 tiara, H., Faroe Channel. 



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



Fia. 27. 



Challengeron armatum, Borg. x 225 

 The mouth (M) of the perforated shell is 



