Description: Body ellipsoidal, 35 to 45 microns long, 24 to 32 microns wide, with a narrow slit-like aperture on the proximal surface extending nearly the full length of the body, and with a sheet-like crescent shaped flap crossing the distal surface diagonally. In lateral view, the proximal surface is somewhat less convex than the distal surface, but the latter is not
strongly arched. Body surrounded completely by a zona having a more or less elliptical outline in proximaldistal view, and having its major axis oblique to that of the body. The zona, therefore, is wider (6 to 10 microns) across the narrow ends of the body than along
its sides (2 to 5 microns), and the two halves of the zona are inverse mirror images of each other. Zona narrowest at the places where the proximal flap merges with it.
Body wall consists of a single, homogeneous, unornamented layer, about 1 micron thick, to which an outer, distinctively textured wall, up to 3 microns thick, is attached on the proximal surface only. The equatorial edge of the outer wall is separated from the
zona by a trough-like depression 2 to 3 microns wide (indicated by arrow on plate 1, figure 17b). Superficial layer of the outer proximal wall, of the zona and of the flap is smooth, but the core of the same structures is granular. In some specimens, one to four small, fingerlike projections or short ridges, textured like the core ofthe zona, arise from the distal surface, generally near the equator and/or close to the flap (see plate 2,
figure 4). Over-all size of specimens from 44 to 60 microns in length, from 28 to 40 microns in width and up to 55 microns in height, including the flap.