8. With two body layers noticeable; rays larger towards the body, tapering 



outwards 



Actinosphaerium Stein 

 Body appearing to be a mass of bubbles; rays entirely hair'like 

 Actinophrys Ehrenberg 



9. Pseudopodia hair'like, often branching 10. 

 Pseudopodia broad or finger'like 15. 



10. Shell with the opening at one side of the end 11. 

 Shell symmetrical 12. 



11. With a narow neck curved to one side, bearing the mouth; shell chitin- 



ous, with small plates 



Cyphodena Schlumberger 

 End of shell bearing the mouth oblique; shell with siliceous plates 

 Trinema Dujardin 



12. Shell spherical, with many small, windowlike apertures from which the 



rays protrude; usually on the end of a stem 

 Clathrulina Cienkowski 

 Shell inverted cup' or vase-shaped, with one opening from which the 

 rays protrude ; no stem 13. 



13. Shell with attached sand grains and similar material 



Pseudodifflugia Schlumberger 

 Shell with definite plates 14. 



14. Opening of shell with prominent sawtooth edges; shell usually with 



spines 



Euglypha Dujardin 

 Opening of shell with minute serrations; no spines 

 Assulina Ehrenberg 



15. Shell discoidal or hemispherical, often resembling a doughnut when seen 



from above; color often brown 16. 



Shell usually bottle- or flask-shaped; colored or not 18. 



16. Shell smooth, without sand grains or foreign material 



Arcella Ehrenberg 

 Shell coated with sand or foreign material 17. 



17. Shell hemispherical, with a large opening in the middle of the flat side 



Phryganella Penard 

 Shell discoidal, compressed laterally, with the opening on one side^ 

 eccentric 



Centropyxis Stein 



18. Shell transparent, without sand grains and not divided into plates 



Hyalosphenia Stein 

 Shell with plates or with attached sand grains or similar material 19. 



19. Shell coated with sand grains or similar material 20. 

 Shell composed of chitinous plates 23. 



20. Shell not constricted by an internal granular collar; shell usually pear- 



shaped 21. 



Opening of shell constricted by an internal granular collar; shell usually 



elliptical 22, 



21. With opening at one end only 



Difflugia Leclerc 

 With openings at both ends 



Amphitrema Archer 



38 



