SUMMARYThree new species ofPythiumare described. The proposed names reflect some of their conspicuous peculiarities:P. coloratum—the yellow oospore and its very thick bluish-lilac wall;P. dissimile—small, usually toruloid compound sporangia and small plerotic oogonia without antheridia;P. pyrilobum—large oogonia and large pyriform sporangial elements combined to hyphal elements without septa.P. pyrilobumis also conspicuous because of its numerous antheridia and entanglements of their stalks, and its distinctly yellow oospores. Each of the latter two species possesses variously shaped sporangia, thus supporting arguments against division of the genus on the basis of sporangial shape.