No. 2.] FRESH-WATER PROTOZOA. 1 3 



Shell chitinous with a few grains of sand at one end 



Heleopera 

 Shell with no sand grains 16 



16. Body spiral Lecquereusia* 



Body not spiral 17 



17. Shell made of four-sided plates; pear-shaped. .Quadrula* 

 Shell of round, irregular, chitinous plates ; com- 

 pressed ; with a two-lipped mouth Nehela 



18. Shell with one pseudopod opening 19 



Shell with two pseudopod openings 27 



19. Shell with evident structure 20 



Shell without evident structure 23 



20. Shell made of grains of sand 21 



Shell chitinous but encrusted with sand grains ; re- 

 tort-shaped, with two lateral processes above .... 



Campascus 

 Shell chitinous, without sand grains 22 



21. Pseudopodia of one kind PseiidodiMugia 



Pseudopodia of two kinds Diaphoropodon 



22. Shell circular, compressed ; mouth irregularly 



notched Assulina 



Shell pear-shaped or spherical ; compressed ; made of 

 rounded, spirally arranged plates, giving an hexa- 

 gonal appearance ; mouth with toothed plates .... 



Ettglypha* 



Shell as above, but with mouth excentric Trinema 



Shell with finer markings ; neck bent to one side .... 



Cyphoderia* 



23. Solitary 24 



Mostly colonial 25 



24. Mouth lateral ; shell thin, flexible ; pseudopodia aris- 



ing from a stalk in the mouth Lieberkuhnia 



Mouth terminal ; shell ovate to spherical, or flattened ; 

 pseudopodia partly reticular, partly branched, 

 sHghtly anastomosing, and extending around the 



body Gromia 



Mouth terminal ; shell very delicate ; pseudopodia 

 not extending around the body Pamphagus* 



25. Shell close to the body; spherical Lecythium 



Shell not close to the body 26 



