386 PROTOZOOLOGY 



composed of quartz grains; colorless to brown; cytoplasm colorless; 

 80-340;u long; in the ooze of ponds and in soil. 



D. corona Wallich. Test ovoid to spheroid, circular in cress- 

 section; crown broadly rounded, with a variable number of spines, 

 aperture more or less convex in profile, central and its border mul- 

 tidentate or multilobate; test with fine sand-grains, opaque; cyto- 

 plasm colorless; pseudopodia numerous, long, branching or bifur- 

 cating; 180-230^4 by about 150/1 ; in fresh water. 



Genus Centropyxis Stein. Test circular, ovoid, or discoid; aper- 

 ture eccentric, circular or ovoidal, often with a lobate border; with 

 or without spines; cytoplasm colorless; pseudopodia digitate; fresh 

 water. 



C. aculeata S. (Fig. 180, g). Test variable in contour and size; with 

 4-6 spines; opaque or semitransparent ; with fine sand-grains or 

 diatom shells; pseudopodia sometimes knotted or branching; when 

 encysted, the body assumes a spherical form in wider part of test; 

 granulated, colorless or with green globules; diameter lOO-lSOju; 

 aperture 50-60^ in diameter. 



Genus Campascus Leidy. Test retort-shaped with curved neck, 

 rounded triangular in cross-section; aperture circular, oblique, with 

 a thin transparent discoid collar; nucleus large; 1 or more contrac- 

 tile vacuoles; body does not fill the test; fresh water. 



C. cornutus L. (Fig. 180, h). Test pale-yellow, retort-form; with 

 a covering of small sand particles; triangular in cross-section; a 

 single nucleus and contractile vacuole; filopodia straight; 110-140/i 

 long; aperture 24-28/; in diameter; in the ooze of mountain lakes. 



Genus Cucurbitella Penard. Test ovoid with sand-grains, not 

 compressed; aperture terminal, circular, surrounded by a 4-lobed 

 annular collar; cytoplasm grayish, with zoochlorellae; nucleus 

 large; 1 to many contractile vacuoles; pseudopodia numerous, 

 digitate ; fresh water. 



C. mespiliformis P. (Fig. 180, i). 115-140/x long; diameter 80- 

 105/1 ; in the ooze or on vegetaiton in ponds and ditches. 



Genus Plagiopyxis Penard. Test subcircular in front view; ovoid 

 in profile; aperture linear or lunate; cytoplasm gray, with a single 

 nucleus and a contractile vacuole; fresh water. 



P. callida P. (Fig. 181, a). Test gray, yellowish, or brown; large 

 nucleus vesicular; pseudopodia numerous, radiating, short, pointed 

 or palmate; diameter 55-135/i; in vegetation. 



Genus Pontigulasia Rhumbler. Test similar to that of Difflugia, 

 but with a constriction of neck and internally a diaphragm made of 

 the same substances as those of the test. 



