SUMMARYThe resting spore ofPhlyctochytrium planicorneenlarges within a resting sporangium, distends it, and discharges endogenously cleaved planonts which cluster at the orifice. InP. aureliae, the resting spore functions directly as a sporangium, and the endogenously cleaved planonts swim at once upon release. The thallus form ofNowakowskiella elegansis influenced by substratum, but resting spore development and discharge pattern are identical in all forms. The resting spore functions as an operculate sporangium or a prosporangium; planonts are cleaved endogenously or in part exogenously, and cluster at the orifice before swimming.Nowakowskiella crassa, N. delica, andN. profusaare reduced to synonymy underN. elegans.