32 (31) Conspicuous unciliated buccal cavity between zone of mem- 



branelles and large undulating membrane 33 



32 (31) Essentially no unciliated surface between right border of zone of 

 membranelles and adjacent ciliary rows 



33 (32) Buccal cavity triangular. Macronucleus usually beaded. Family CON- 

 DYLOSTOMATIDAE. 



33 (32) Buccal cavity circular. Macronucleus ribbonlike. Family CHATTONI- 

 DIIDAE. 



34 (32) Zone of membranelles apical, spiraled, enclosing ciliated field. Family 

 STENTORIDAE. 



34 (32) Zone of membranelles longitudinal, or spiraled, and not apical 35 



16 



