Difflugia scalpellum Penard, 1899
Synonym: D. smilion Thomas, 1953
Diagnosis: Shell bilateral symmetrical, cylindrical, gradually swelling from the aperture for about two-thirds of the body length to the broadest diameter and then tapering in the last third of the body length to a bluntly or sharply, asymmetrically shaped apex. Test composed of quartz particles and diatom frustules, giving it the appearance of a regular smooth surface. Aperture usually circular. Nucleus vesicular with central nucleolus.
Dimensions: Penard (1899): 260-300 µm, in one place the average length was 220-230 µm; Penard (1902): average length 250 µm, length up to 300 µm; my measurements: 212-263 µm.
Ecology: Freshwater. Penard found this species only in deep lakes, at a depth of 30-100 m. I found it in ditches and ponds, also between sphagnum.
Remarks: The structure of the nucleus, vesicular, is quite remarkable for such a large species. All other known large Difflugia species have ovular nuclei, as far as we know. This species was described and pictured by Ogden as Difflugia venusta Penard 1902, but his photomicrographs are quite different from Penards drawing and description.