Naked, or not inclosed in a shell.

11. Cercaria: caudatum. With a tail.

12. Leucophra: ciliatum undique. Every part ciliated.

13. Trichoda: crinitum. Hairy.

14. Kerona: corniculatum. With horns.

15. Himantopus: cirratum. Cirrated, or curled.

16. Vorticella: ciliatum apice. The apex ciliated.

Covered with a shell.

17. Brachionus: ciliatum apice. The apex ciliated.

I. MONAS.