238 HANDBOOK OF PROTOZOOLOGY 



brown. The cytoplasm is colorless. Length 80 to 340 microns. 

 In the ooze of ponds and in soil. 



Genus Centropyxis Stein. Test circular, ovoid, or discoid. 

 Aperture eccentric, circular or ovoidal, often with a lobate 

 border. With or without spines. The cytoplasm is colorless; 

 pseudopodia digitate. 



Centropyxis aculeata Stein (Fig. 95,/). Test variable in con- 

 tour and size; with 4 to 6 spines; opaque or semi-translucent; 

 with fine sand-grains or diatom shells. Pseudopodia sometimes 

 knotted or branching. When encysted, the protoplasm assumes 

 a spherical form in the thicker part of the test ; granulated, color- 

 less or with green globules. Diameter 100 to 150 microns; aper- 

 ture 50 to 60 microns. 



Genus Cucurbitella Penard. Test ovoid with sand grains, 

 not compressed; aperture terminal, circular, surrounded by a 

 four-lobed annular collar. The cytoplasm is grey, granular, and 

 contains symbionts, the Zoochlorellae. A single large nucleus; 

 one to many contractile vacuoles; pseudopodia numerous, 

 digitate. 



Cucurbitella mespiliformis Penard (Fig. 95, g). Length 115 

 to 140 microns; diameter 80 to 105 microns. In the ooze or on 

 vegetation in ponds and ditches. 



Genus Plagiopyxis Penard. Test sub-circular in dorsal view; 

 ovoid in profile; aperture linear or lunate. Cytoplasm grey, 

 with a single nucleus and a contractile vacuole. 



Plagiopyxis callida Penard (Fig. 95, h). Test grey, yellowish, 

 or brown. A large vesicular nucleus; pseudopodia numerous, 

 radiating, short, pointed or palmate. Diameter 55 to 135 

 microns. 



Genus Pontigulasia Rhumbler. Test similar to that of 

 DifBugia, but with a constriction of the neck and internal to it, 

 a diaphragm made of the same substances as those of the test. 



Pontigulasia vas (Leidy) (Fig. 95, i). Test rounded or ovoid, 

 constriction deep and well-marked; with sand-grains and other 

 material. Aperture terminal. Length 125 to 170 microns. 

 Fresh water ponds. 



Genus Phryganella Penard. Test spheroidal to ovoid, with 

 sand-grains and minute diatom shells. Aperture terminal, 



