TESTACEA 391 



and food particles; 2 contractile vacuoles; 60-200/x long; diameter 

 30-70/x. Several varieties. 



Genus Trinema Dujardin. Test small, hyaline, ovoid, compressed 

 anteriorly, with circular siliceous scales; aperture circular, oblique, 

 invaginate; nucleus posterior; filopodia not branched; fresh water in 

 vegetation. 



T. enchelys (Ehrenberg) (Fig. 183, a). 1-2 contractile vacuoles; 

 pseudopodia attenuate, radiating; 30-100)u long; IS-GOju wide; scales 

 4-12;u in diameter. 



Genus Corythion Taranek. Test small, hyaline, composed of small 

 oval siliceous plates; compressed; elliptical in cross-section; aperture 

 subterminal, ventral or oblique, and circular or oval; numerous 

 filopodia; fresh water. 



C. pulchellum Penard (Fig. 182, e, /). Aperture lenticular; cyto- 

 plasm colorless; 2-3 contractile vacuoles; 25-35/x by 15-20ju; aper- 

 ture 7-1 0/x by 3-4/x. 



Genus Placocista Leidy. Test ovoid, hyaline, compressed; len- 

 ticular in cross-section; with oval or subcircular siliceous scales; 

 aperture wide, linear, with flexible undulate borders; nucleus large, 

 posterior; often with zoochlorellae; filopodia branching and many, 

 generally arising from a protruded portion of cytoplasm; fresh 

 water. 



P. spinosa (Carter) (Fig. 183, h). Margin of test with spines, 

 either singly or in pairs; 116-174)u by 70-100^; in sphagnum. 



Genus Assulina Ehrenberg. Test colorless or brown; ovoid; with 

 elliptical scales, arranged in diagonal rows; aperture oval, terminal 

 bordered by a thin chitinous dentate membrane; nucleus posterior; 

 contractile vacuoles; filopodia divergent, sometimes branching; fresh 

 water. 



A. seminulum (E.) (Fig. 183, c). Body does not fill the test; with 

 numerous food particles; pseudopodia few, straight, divergent, 

 slender, seldom branched; 60-150/^ by 50-75/^; in sphagnum. 



Genus Nebela Leidy. Test thin, ovate or pyriform; with circular 

 or oval platelets of uniform or various sizes; highly irregular; endo- 

 plasm with oil globules; nucleus posterior; body does not fill the 

 test, and is connected with the latter by many ectoplasmic strands 

 at fundus end; pseudopodia blunt, rarely branched; fresh water. 

 Numerous species. 



N. collaris (Ehrenberg) (Fig. 183, d). Test pyriform, fundus obtuse 

 in profile; aperture without any notch; endoplasm with chlorophyl- 

 lous food particles; pseudopodia digitate, short, usually 3-6 in num- 

 ber; about 130)u by 85-90yu; in marshes among sphagnum. 



