TESTACEA 



489 



cross-section; aperture circular; cytoplasm gray, with many granules 

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

 30-70/*. 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. 207, a). 1-2 contractile vacuoles; 



Fig. 207. a, Trinema enchelys, X330 (Wailes); b, Placocista spinosa, 

 X200 (Wailes); c, Assulina seminulum, X400 (Wailes); d, Nebela collaris, 

 X200 (Cash); e, Quadrula symmetrica, X200 (Gash); f, Sphenoderia 

 lenta, X330 (Leidy). 



pseudo podia attenuate, radiating; 30-100/z long; 15-60/x wide; scales 

 4-12/x in diameter. 



T. lineare Penard (Fig. 79). Test transparent; scales indistinct; 

 about 35/x by 17/t; filopodia. Sexual fusion (Dunkerly, 1923) (p. 183). 



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. 206, e, /). Aperture lenticular; cyto- 

 plasm colorless; 2-3 contractile vacuoles; 25-35/z by 15-20/z; 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, 



