often tube-forming

Eight frontal and 3 caudal cirri; Genus _Gonostomum_
not tubiculous

4. Anal cirri present; with or Genus *_Epiclintes_
without short lateral bristles

Anal cirri absent; no bristles Genus _Uroleptus_

5. With frontal cirri 6

No frontal cirri; 2 to 3 rows of Genus _Holosticha_
ventral cirri; anal cirri small

6. Right margin of peristome straight Genus _Oxytricha_
as far as the anterior end; 5 rows
ventral cirri; 5 anal cirri

Right margin of peristome curved 7

7. Five rows or less of ventral cirri 8

More than 5 rows of ventral cirri Genus _Urostyla_

8. Membranelles normal; 5-10 anal Genus *_Amphisia_
cirri; no caudal cirri

Membranelles normal; 5 to 10 anal Genus _Stylonychia_
cirri; 3 caudal cirri