Family _Rhizomastigidæ_:

1. Flagellum repeatedly thrown off Genus *_Mastigamoeba_
and reassumed in part

2. Flagellum never thrown off 3

3. a. Pseudopodia lobose Genus _Mastigamoeba_

b. Pseudopodia ray-like Genus _Mastigophrys_

Family _Codonoecidæ_:

1. Goblet-shaped cups adherent Genus *_Codonoeca_
by stalk

Family _Heteromonadidæ_:

1. The long flagellum vibratory Genus *_Monas_

2. The long flagellum rigid; Genus _Sterromonas_
shorter one vibrates

* Presence at Woods Hole indicated by asterisk.


KEY TO MARINE QENERA OF CHOANOFLAGELLIDA.

1. Without gelatinous 3