144 THE RADIOLARIA 



CLASSIFICATION. 1 



CLASS RADIOLARIA. 



SUB-CLASS I. PERIPYLARIA (Spumellaria). 



Central capsule homaxonic, uniformly perforated by numerous similar 

 and extremely small pores. Skeleton siliceous, Extra-capsulum volum- 

 inous (except in Physematiidae). 



ORDER 1. Collodaria. 



Large monozoic forms not forming a true coenobium. Skeleton absent 

 or spicular. 



FAMILY 1. PHYSEMATIIDAE. Large vacuoles confined to the endoplasm. 

 No stratified concretions in the latter. No pigment. Few "yellow cells." 

 Nucleus spherical, with smooth membrane and a few rounded nucleoli. 

 Selected forms : Physematium mulleri, H. ; TJialassolampe margarodes, H. r 

 Mediterranean and Canary Islands ; Lampoxanthium murrayanum, Fowl., 

 Faroe Channel. The genus Actissa of Haeckel is an early stage of growth 

 of some species of this family. 



FAMILY 2. THALASSOPHYSIDAE. Large vacuoles extracapsular. 

 Structure similar to that of the Thalassicollidae, but nuclear membrane 

 usually tubercular or papillary. Reproduction by rapid and peculiar 

 fragmentation (Fig. 21). Spores unknown. Selected forms : Thalas- 

 siosolen atlanticus,Wo\f. (28); Thalassophysa pelagica, H. (Fig. 1), Faroe 

 Channel ; T. sanyuinoknta, H. ; T. papillosa, H., Mediterranean and 

 Canary Islands (often deformed by ingested Coccolithophoridae). For 

 further account of this family see Brandt (25). 



FAMILY 3. THALASSICOLLIDAE. Nuclear membrarne smooth and 

 spherical. Stratified concretions present in the endoplasm. Multiplica- 

 tion by binary fission, by isospores, and by heterospores (see Fig. 2 j 

 Brandt [25, 25a, and 26]). Selected forms : Thalassicolla nucleata, Hux., 

 Valencia Harbour, Faroe Channel, and cosmopolitan ; T. spumida, H., 

 Canary Islands ; T. pellucida, H., cosmopolitan. 



FAMILY 4. THALASSOTHAMNIDAE, Hacker (37). Skeleton in the 

 form of a large single radiate spiculum or of a double spiculum. Central 

 capsule sometimes spherical, characteristically lobed or branched. 

 Nucleus complex. Nuclear membrane crenate (Fig. 14). Endoplasm with 

 stratified inclusions. Selected forms : TJialassothamnus ramosus, Hack., 

 Antarctic ; Cytocladiis spinosus, Schroder (Fig. 10), Japan Seas (38). 



FAMILY 5. OROSPHAERIDAE. Protoplasm organised as in the preceding 

 family. Skeleton a perforated shell with branched and thorny spines. 

 Orosphaera, H., deep water of mid- Atlantic. This family has been re- 

 moved by Hacker (37) from the Phaeodaria, with which group Haeckel 

 associated it ; but if the presence of a phaeodium, astropyle, and parapyles 

 is confirmed, its systematic position will have to be revised. 



1 The number of genera and species in this class is so large that only a selection 

 can be referred to here. North Atlantic forms have been chiefly selected. 



