TESTACEA 



379 



Of several varieties, two may here be mentioned; var. angulosa 

 (Perty), test smaller, 30-40/x in diameter, faceted, forming a 5- to 

 8-sided figure, with obtuse angles; var. gibbosa (Penard), test gib- 

 bous, surface pitted with circular depressions of uniform dimensions; 

 45-50/x up to 100/x in diameter. 



A. discoides E. (Fig. 177, c). Test circular in front view, plano- 

 convex in profile; diameter about 3-4 times the height; test color- 

 ation and body structure similar to those of A. vulgaris; test 70- 

 260^ in diameter; in fresh w^ater. 



Fig. 177. a, b, Arcella vidgaris, Xl70; X230 (Leidy); c, A. discoides, 

 X170 (Leidy); d, A. mitrata, Xl40 (Leidy); e, f, A. catinus. X 170 (Cash); 

 g-i, A. dentata, Xl70 (Leidy); j, k, A. artocrea, Xl70 (Leidy). 



A. mitrata Leidy (Fig. 177, d). Test balloon-shaped or polyhedral; 

 height exceeds diameter of base; aperture circular, crenulated and 

 usually evarted within inverted funnel; protoplasmic body sphe- 

 roidal, wdth 'neck' to aperture and cj^toplasmic strands to test; 6 or 

 more slender lobopodia; test 100-145;u high, 100-152/i in diameter; 

 in fresh water among vegetation. 



A. catinus Penard (Fig. 177, e, /). Test oval or quadrate, not 

 circular, in front view; aperture oval; dome compressed; lateral 

 margin with 6 or 8 facets; test 100-120^ in diameter and about 

 45/i high; fresh water among vegetation. 



A. dentata Ehrenberg (Fig. 177, g-i). Test circular and dentate 



