Difflugia oblonga group
In 1838 Christian Gottfried Ehrenberg published a short but clear description of a testate amoeba which he named Difflugia oblonga and which had following characters: shell oblong (=ovoid-elongate), rounded fundus, smooth, 110 µm long and brownish. To date this fairly general description has led to different interpretations and alternations by several authors, which identified it with Difflugia pyriformis and or D. proteiformis. See my comments on D. oblonga.
Though it is impossible now to apply the name D. oblonga to any existing species, there still exist some species one of which could have been under observation and described as D. oblonga by Ehrenberg. Typical oblong species are D. lanceolata and D. bryophila. Oblong species are not always easy to distinguish from each other solely based on light microscopical characters. DNA sequencing can be very helpful here. In fact we don't know how many cryptic species there are. Therefore these forms and species are part of a complex.