Family _Bodonidæ_:
1. Body very plastic, Genus *_Bodo_
almost amoeboid
Body not plastic; with large Genus *_Oxyrrhis_
anterior cavity, holding flagella
Family _Trimastigidæ_:
1. With an undulatory membrane Genus _Trimastix_
between accessory flagella
Without such membrane; flagella Genus _Costia_
contained in a ventral groove
while at rest
* Presence at Woods Hole indicated by asterisk.