No. 2.] FRESH-WATER PROTOZOA. I7 



CLASS HELIOZOA. 

 Key to Genera. 



1. No outer envelope. 2 



Outer envelope present 6 



2. Body commonly amoeboid ; pseudopodia either from 



all sides or from one place ; no axial fiber 3 



Spherical ; pseudopodia from all sides, with axial fiber 5 



3. Ectoplasm and entoplasm not differentiated ; color- 



less 4 



Ectoplasm and entoplasm differentiated ; the first 

 hyaline, and the latter red or brown. Commonly 

 red cysts on algae Vampyrella* 



4. Nuclei one or more ; several slowly pulsating vacu- 



oles ; solitary Nuclearia* 



Colonies of eight or less; pseudopodia with spindle 

 swellings Monobia 



5. The vacuolated ectoplasm not sharply separate from 



entoplasm ; central nucleus Actinophrys* 



Ectoplasm with large vacuoles, sharply separate from 



entoplasm ; many nuclei ; i mm. in size 



A ctinospliierium 



6. Envelope jelly-like; streaked, punctured, or folded. . 7 

 Envelope of isolated silicious pieces, or a silicious 



shell 8 



7. Envelope punctured, with fine radiating spines be- 



tween the pseudopodia Heterophrys 



Envelope of streaked appearance, lobe-like surface; 

 colonial Sphcerastrum 



8. Envelope of many layers of silicious globules 



Pompholyxophrys 

 Envelope of loose and more or less bent silicious 



needles ; commonly colonial Raphidiophrys* 



Envelope of leaf-like, pointed silicious plates 



Pinaciophora 



Envelope of radiate spines, with a basal plate 



Acanthocystis 

 Envelope of silicious shell, with rounded openings. . 



Clathrulina* 



2 



