Heleopera petricola Leidy, 1879
Diagnosis: Shell strongly compressed, especially near the aperture, relatively narrow, mostly colorless, sometimes light yellow or light violet; shell mostly irregular, sometimes with a regular pattern, covered with amorphous scales or siliceous plates which form a loose reticulation with the fundus provided with sand grains; outline subject to much variation, but generally the aperture is 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 Sphagnum or moss in boggy places.
Remarks: Several forms of this species have been described by Cash et al, (1909); Bonnet and Thomas (1955) which differ in size, structure and color. Cash et al. (1909) suggest that variations in this species are such that they all tend to merge into each other.