IIELIOZOA 



251 



Solitary, active. Diameter 25 to vS5 microns. Outer envelope 

 5 to 10 microns larger. In pools. 



Genus Acanthocystis Carter. Spherical without mucila- 

 ginous mantle, but with silicious scales arranged tangentially 

 and radiating silicious spines with ends pointed or bifurcated. 

 Nucleus and endoplasm eccentric. The central granule distinct. 

 Several species. 



Fig. 100 a. Pompholyxophrys punicea. XI 70 (After West). 



b. Acanthocystis aculeata. X200 (After Stern). 



c. Raphidiophrys pallida. X200 (After Penard). 



d. Raphidiocystis tubifera. X330 (After Penard). 



e. Wagnerella borealis. X50 (After Kiihn). 



f. Pinaciophora fluviatilis. X165 (After Penard). 



Acanthocystis aculeata Hertwig and Lesser (Fig. 100, h). 

 Tangential scales stout and pointed, curved and nail-headed. 

 The cytoplasm greyish; nucleus eccentric; a single contractile 

 vacuole. Diameter 35 to 40 microns. Spines about one-third 

 the diameter of body. In lakes, ponds, and pools. 



Genus Raphidiophrys Archer. Spherical. Mucilaginous en- 

 velope with spindle-shaped or discoidal spicules which extend 

 normally outwards along the pseudopodia. Nucleus and 

 endoplasm eccentric. Solitary or colonial. Several species. 



Raphidiophrys pallida Schulze (Fig. 100, c). Outer gela- 

 tinous envelope crowded with curved lenticular spicules, form- 



