380 PROTOZOOLOGY 



in front view, crown-like in profile; diameter more than twice the 

 height; aperture circular, large; colorless to brown; about 95/i in 

 diameter, aperture SO/z in diameter; 15-17 spines; in the ooze of 

 freshwater ponds. 



A. artocrea Leidy (Fig. 177, j, k). Height of test 1/4-1/2 the diame- 

 ter; dome convex; surface mammillated or pitted; border of test 

 everted and rising 1/4-1/2 the height of test; about 175ju in diame- 

 ter; fresh water. 



Fig. 178, a, b, Pyxidicula operculata, X800 (Penard); c, Pseudochlaniys 

 patella, X330 (Cash); d, e, Diflugiella apiculata, X270 (Cash); f, Crypto- 

 difflugia oviformis, X320 (Cash); g, Lesquereusia spiralis, X270 (West); 

 h, Hyalosphenia papilio, X330 (Leidy); i, Corycia coronata, Xl70 

 (Penard); j, Pamphagus mutahilis, X330 (Leidy); k, Plagiophrys parvi- 

 punctata, X330 (Penard). 



Genus Pyxidicula Ehrenberg. Test patelliform; rigid, transparent, 

 punctate; aperture circular, almost the entire diameter of test; 

 cytoplasm similar to that of Arcella; a single nucleus; 1 or more 

 contractile vacuoles; fresh water. 



P. operculata (Agardh) (Fig. 178, o, b). Test smooth, colorless to 



