Centropyxis ecornis  (Ehrenberg, 1841) Leidy, 1879

Diagnosis: Shell of large size, usually more than 200 µm, usually circular or largely elliptical, mostly irregular in outline; in lateral view the dorsal region is spherical and tapers from the mid-body position to the apertural lip; shell rough, covered with quartz sand grains, embedded in an organic cement; color usually grey, sometimes brownish, depending upon the density of the xenosomes; aperture invaginated, oval or circular, irregularly lobed, not very much eccentric, with a thick apertural rim.

Dimensions: Literature 199-316 µm, mean 211 µm; my measurements 167-356 µm.

Habitat: Freshwater; in sediments and among water plants and mosses.

Remarks: This species is not well defined. The name means: “without spines”. Probably several species are covered by the name C. ecornis. C. cordobensis and C. lapponica might have been confused with this species.