74 (73) No aboral adhesive disc. Migratory motile stages of ciliates of order Peri- 

 trichida, suborder Sessilina. 



75 (7 A) Skeletal ring with 20-50 smooth links. Subfamily Urceolarinae. 





75 (74) Skeletal ring of hooked or spiked links. Subfamily 

 Trichodininae. 



76 (73) Cytostome on ventral surface, not surrounded by zone of membranelles. 

 Family HALTERIIDAE. 



76 (73) Cytostome apical, enclosed within spiral zone of membranelles. Family 

 STROBILIDIIDAE. 



77 (72) Zone of membranelles winding at least 360° to anteroventral cytostome. 

 Family LICNOPHORIDAE. 



77 (72) Buccal cilia not in a clockwise zone of membranelles 78 



29 



