Heleopera petricola Leidy, 1879

Diagnosis: Shell strongly compressed, especially near the aperture; relatively narrow; mostly colorless, sometimes light yellow or light violet. Test generally irregular, occasionally showing a more regular pattern, and covered with amorphous scales or siliceous plates forming a loose reticulation, with the fundus often containing sand grains. Outline highly variable, but the aperture is usually convex or, when cut straight across, more or less rounded at the corners.

Dimensions: Literature: length 70–150 µm.
My measurements: 105–142 µm.

Ecology: Common species. Habitat in Sphagnum or moss in boggy places.

Remarks: Several forms of this species have been described by Cash et al. (1909) and Bonnet & Thomas (1955), differing in size, structure, and color. Cash et al. (1909) noted that the variation within this species is such that the forms tend to merge into one another.