226 HANDBOOK OF PROTOZOOLOGY ^ 



Test simple and membranous , . " ; 



Pseudopodia filose or simply branched Family 1 Arcellida'e 



Pseudopodra.reticulate , . . ." Family 2 Allogromiidae 



Test with foreign bodies, plates, or scales ., 



Chitinous test with foreign bodies Family 3 Difflugiidae 



Chitinous test with platelets or scales '. . . .Family 4 Euglyphidae 



Family 1 Arcellidae Schulze 



The generic differentiation of the family is based mainly 

 upon the form and structure of the test. ^ 



Genus Arcella Ehrenberg-. • Test tra«sparent, chitinous, 

 •colorless to brown (when old), and densely punctafted. In 

 dorsal view it is circular, angular, or stellate; in profile plano- 

 convex to hemispherical. Variously ornamented. Apertu/e 

 circular, central, and inverted like a funnel. Occasionally 

 spinous. The protoplasmic body does not fill the test and is 

 connected wi^^ the latter by ectoplasmic s-trands. Pseudopodia 

 few, digitate,-blunt, simple or branched. Two nuclei, chromidia, 

 and several contractile vacuoles. Fresh water. Numerous 

 species. 



A rcella vulgaris Ehrenberg (Figs. 4 ; 89, a) . Height of test about 

 one-half the diameter. Hemispherical. Dome evenly convex; 

 aperture central and circular. Test colorless, yellow, or brown. 

 The protoplasmic body conforms with the shape of the test, 

 but does not fill the latter. Pseudopodia are lobose and hyaline. 

 Two vesicular nuclei; numerous food vacuoles, chromidia, and 

 contractile vacuoles conspicuously present. Diameter of test 

 50 to 150 microns. In the ooze of stagnant water and on sub- 

 merged plants. Also in moist soil. Cosmopolitan. 



Arcella dentata Ehrenberg (Fig. 89, h). Test in aperture 

 view 'circular and dentate; in profile crown-like. Diameter 

 more than twice the height. Aperture circular and large. Color- 

 less to brown. The .protoplasm as in A. vidgaris. Diameter of 

 test 130 to 200 microns. In the ooze of fresh water ponds. 



Arcella discoides Ehrenberg (Fig. 89, c). Test circular in 

 aperture view; plano-convex in profile. Diameter is about 

 three or four times the height. Test coloration and body struc- 

 ture similar to those of the last two species. Diameter of test 

 70 to 260 microns. In ponds and niarshes. 



Genus Pyxidicula Ehrenberg. Test patelliform ; rigid, trans- 



