9 (8) Clear vacuole filling posterior end of cell. Cilia closely set, apparently in 

 whorls. Vase-shaped lorica present or absent. Surface firm, with rectan- 

 gular alveoli. Family METACYSTIDAE. 



9 (8) Clear vacuole not filling posterior end of cell. Never with lorica 10 



10 (9) Ciliary rows spiraled when cell contracts. Macronucleus var- 

 iously shaped with normal Feulgen reaction. Shapes various; 

 behavior generally nonthigmotactic. Family ENCHELYIDAE. 



10 (9) No spiral contraction. Nuclei largely Feulgen negative. Animal generally 

 highly thigmotactic, contractile, fragile, and snakelike in shape. Family 

 TRACHELOCERCIDAE in part (also see couplet 95). 



11 (4) Cytostome not in vestibulum. 



12 



11 (4) Cytostome in vestibulum 14 



