CT: Cryptodifflugia operculata n. sp. is a small shelled rhizopod differing from the type species of the genus, C. oviformis Penard, 1890, chiefly in its manner of encysting with a secreted operculum closing the aperture of the test. Locomotion is by means of finely lobose, hyaline pseudopodia. The transparent, rigid test, which shatters under pressure, was found to consist at least in part of polysaccharide. Nuclear division is by typical mitosis, and simple cell division was the only method of reproduction observed. A definition of the genus Cryptodifflugia consistent with Penard's descriptions and distinguishing it clearly from the genus Difflugiella is offered, and a provisional key to the genus is prese